American Journal of Epidemiology

This Article Abstract FREE Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (54) Request Permissions Disclaimer Google Scholar Articles by Kilkkinen, A. Articles by Adlercreutz, H. Search for Related Content PubMed PubMed Citation Articles by Kilkkinen, A. Articles by Adlercreutz, H. Social Bookmarking          What's this?

American Journal of Epidemiology Vol. 155, No. 5 : 472-477
Copyright © 2002 by The Johns Hopkins University School of Hygiene and Public Health

ORIGINAL CONTRIBUTIONS

Use of Oral Antimicrobials Decreases Serum Enterolactone Concentration

Annamari Kilkkinen¹, Pirjo Pietinen¹, Timo Klaukka², Jarmo Virtamo¹, Pasi Korhonen¹ and Herman Adlercreutz^3,4

¹ Department of Epidemiology and Health Promotion, National Public Health Institute, Helsinki, Finland.
² Research and Development Unit, Social Insurance Institution, Helsinki, Finland.
³ Institute for Preventive Medicine, Nutrition and Cancer, Folkhälsan Research Center, Helsinki, Finland.
⁴ Department of Clinical Chemistry, University of Helsinki, Helsinki, Finland.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The lignan enterolactone, a phytoestrogen, may protect against hormone-dependent cancers and cardiovascular diseases. It is produced by the intestinal microflora from dietary precursors. Because of the pronounced impact of antimicrobials on the intestinal microflora, the authors examined whether serum enterolactone concentration is affected by previous use of oral antimicrobials. Enterolactone was measured by time-resolved fluoroimmunoassay in 2,753 Finnish men and women aged 25–64 years who participated in a cross-sectional national survey in 1997. Background information was collected by self-administered questionnaire, and data on antimicrobial treatment were gathered from the nationwide prescription database of the Social Insurance Institution. Serum enterolactone concentration was significantly lower in those who had used oral antimicrobials up to 12–16 months before serum sampling than in nonusers (16.4 vs. 19.3 nmol/liter). The concentration was associated with the number of treatments and the time from the last treatment. Modest differences were present between various antimicrobials. The authors' findings support the crucial role of gut microflora in the metabolism of lignans. Furthermore, recent use of antimicrobials should be considered when the association between serum enterolactone concentration and risk of chronic diseases is studied.

antibiotics; bacteria; biological markers; cross-sectional studies; drug therapy; intestines; lignans; metabolism

Abbreviations: BMI, body mass index; CI, confidence interval; SD, standard deviation; TR-FIA, time-resolved fluoroimmunoassay

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The lignan enterolactone, a phytoestrogen, is a naturally occurring diphenolic compound that has several biologic properties (1–8). The actions of enterolactone provide potential mechanisms for a postulated preventive influence on hormone-dependent cancers and cardiovascular diseases. In animal models, a diet rich in lignans has been shown to protect against these diseases (9, 10); although human studies are scarce, some evidence suggests that enterolactone may lower the risk of breast cancer (11) and acute coronary events (12).

Precursors of mammalian lignans are highly concentrated in flaxseed, with lesser amounts found in other seeds, nuts, whole grains, berries, fruit, and vegetables (13–15). Recently, however, a number of new mammalian lignan precursors have been identified (16). When plant lignans are consumed, they are converted into biologically active mammalian lignans by bacteria in the gut (17–19). The most abundant mammalian lignan is enterolactone. Once absorbed, mammalian lignans are conjugated with glucuronic acid or sulfate in the liver, reexcreted through the bile duct, deconjugated by the bacteria, and reabsorbed (enterohepatic circulation). Lignans are excreted in the urine and feces mainly as glucuronides.

We previously observed that serum enterolactone concentration varies widely in the population and that consumption of lignan-containing foods and health-related variables explain only a small part of this variation (20). This observation suggests a crucial role for the gut in the metabolism of lignans. Because of the pronounced impact of antimicrobials on the intestinal microflora, we investigated the effects of previous use of oral antimicrobials on serum enterolactone in a large population sample.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Subjects
This study is part of a cross-sectional health survey carried out in Finland during early spring 1997. The participants were aged 25–64 years and lived in five areas: the Helsinki metropolitan area in the south, the city of Turku and its surrounding rural communities in the southwest, the provinces of North Karelia and Kuopio in the east, and the province of Oulu in the north. The health survey population (n = 10,000) was randomly drawn from the National Population Register stratified by 10-year age groups, regions, and sex. For the dietary survey, a subsample of 4,000 subjects (40 percent) was randomly allocated; of these subjects, 2,862 participated in the dietary survey (21). A serum sample was available for 2,753 subjects, who thus formed the final study population.

All participants were invited to the local health center, where fasting (minimum 4 hours) venous samples were taken. The samples were fractioned and serum aliquots were stored frozen at -20°C. Weight and height were also measured during the examination, and body mass index (BMI) was computed as weight in kilograms divided by the square of height in meters (kg/m²). Furthermore, the subjects filled in a self-administered questionnaire, which was completed at the examination and contained questions on diet, health, and smoking. Consumption of lignan-containing foods was quantified from the food frequency questionnaire including 38 food items by summing the frequency of consumption, in number of servings per month, of rye bread, crisp bread, porridges, cereals, salad vegetables, roots, legumes, vegetable dishes, fruit, berries, fruit juices, and berry juices.

Data on the use of antimicrobials were based on the nationwide prescription register of the Social Insurance Institution. All prescriptions reimbursed by the National Sickness Insurance Scheme are registered. The database includes information about the patient, drug, and day of purchase. The medication is classified according to the Anatomical Therapeutic Chemical Classification (ATC) system. In this system, the drugs are divided into different groups according to the organ or system on which they act and/or their therapeutic and chemical characteristics (22). Oral antibacterials include tetracyclines, amoxicillin and other extended-spectrum penicillins, phenoxymethylpenicillin and other beta-lactamase-sensitive penicillins, cloxacillin and other beta-lactamase-resistant penicillins, combined penicillins, cephalosporins, sulfonamides and trimethoprims, macrolides and lincosamides, fluoroquinolone antibacterials, and steroid antibacterials.

The health survey was approved by the Ethics Committee of the National Public Health Institute.

Analytical methods
Serum enterolactone concentration was determined from the frozen serum of 2,753 study subjects (1,301 men and 1,452 women) in spring 1998. The enterolactone analysis was performed by time-resolved fluoroimmunoassay (TR-FIA) (23), with slight modifications (24). In brief, the modified method is as follows: 50 µl of serum were incubated with 50 µl of hydrolysis reagent containing sulfatase (Sigma, St. Louis, Missouri) and ß-glucuronidase (Boehringer-Mannheim, Mannheim, Germany) overnight at 37°C. After hydrolysis, 150 µl of 0.5 percent BSA-Tris Buffer (BSA; Merk AG, Darmstadt, Germany), pH 7.8, was added to obtain the optimal pH and protein concentration for analysis. The analyses were performed on anti-rabbit antiserum coated microtitration strips by using 20 µl of sample. Enterolactone concentrations were measured by using the VICTOR 1420 multilabel counter (Wallac Oy, Turku, Finland). Each batch was analyzed with three duplicate quality-control serum samples. The interassay coefficient of variation (percentage) and the concentrations of the samples were 16.8 percent (4 nmol/liter), 10.1 percent (14 nmol/liter), and 13.1 percent (59 nmol/liter). The intra-assay coefficient of variation varied from 6.9 percent to 9.9 percent.

The modified method described above (24) tends to yield 15–30 percent higher results than the standard TR-FIA method with extraction (23). To enable comparison of results with those from previous studies, we derived an equation between the modified TR-FIA method and the standard TR-FIA method by analyzing 92 samples with both methods. The final results were calculated by using the following equation: final concentration in nmol/liter = measured concentration in nmol/liter x 0.934 – 11.03.

Statistical methods
Those subjects who had purchased antimicrobials, according to the Finnish prescription register, from January 1996 to the day of the spring 1997 examination were considered users of antimicrobials; correspondingly, those who had not purchased antimicrobials were categorized as nonusers. Differences in age, BMI, occurrence of constipation, consumption of lignan-containing foods, and smoking habits between users and nonusers were analyzed by using the t test for continuous variables and the ² test for dichotomized variables. A linear regression model was used for investigating the dependence of serum enterolactone concentration on the total number of antimicrobials purchased and on time since the last treatment. To examine the association of serum enterolactone with number of treatments and with time from the last treatment, the subjects were divided into the following four groups: 1) time from the last antimicrobial treatment being a maximum of 3 months and at least two treatments received, 2) time from the last antimicrobial treatment being a maximum of 3 months and only one treatment received, 3) time from the last antimicrobial treatment being more than 3 months and at least two treatments received, and 4) time from the last antimicrobial treatment being more than 3 months and a maximum of one treatment received during the study period. By using the last group as the reference, we tested differences in mean serum enterolactone concentrations with an F-test statistic from the analysis of variance. To examine differences between various antimicrobials, subjects were divided into groups according to the last antimicrobials used during the 3 months preceding the examination. Differences in mean serum enterolactone concentrations were tested with an F-test statistic from the analysis of variance. This analysis was repeated for only those with no prior use of antimicrobials.

Because of the skewness of serum enterolactone concentration distribution, enterolactone values were log-transformed prior to statistical analyses. On the basis of our previous observations (20) that serum enterolactone concentration is positively associated with constipation, consumption of lignan-containing foods, and normal BMI and is negatively associated with smoking, all of these variables were included in the models.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Altogether, 964 subjects (374 men and 590 women) had purchased antimicrobial agents at least once during the time period between January 1996 and the day of the examination in spring 1997. Thus, the proportion of users among the 2,753 study subjects was 35 percent—29 percent of the men and 41 percent of the women. The characteristics of users and nonusers are shown in table 1. No significant differences between these two groups were observed in age, consumption of lignan-containing foods, occurrence of constipation, or smoking. However, male users had a higher BMI than nonusers.

View this table: [in this window] [in a new window]   TABLE 1. Characteristics of the population studied to determine whether use of oral antimicrobials decreases serum enterolactone concentration, Finland, 1997

 
A total of 1,767 antimicrobial prescriptions were purchased, and the number of administrations of antimicrobials per person varied from one to 10. More than half of the users (62 percent of the men and 55 percent of the women) had purchased antimicrobials only once. Two treatments had been received by 23 percent, three treatments by 10 percent, and four or more treatments by 6 percent of the men. The corresponding values for women were 23 percent, 11 percent, and 12 percent. Nearly two thirds of the prescriptions were purchased by female subjects. The mean number of prescriptions did not differ significantly between categories of age, constipation, or smoking, whereas prescriptions were more frequent among overweight men (BMI = 25–35 kg/m²) than their normal-weight counterparts.

Subjects who had used antimicrobials up to 12–16 months before serum sampling had a significantly lower serum enterolactone concentration than nonusers: mean, 16.4 (standard deviation (SD), 14.3) nmol/liter versus mean, 19.3 (SD, 16.1) nmol/liter. The difference was similar for men (mean, 14.4 (SD, 13.0) nmol/liter vs. mean, 17.7 (SD, 14.0) nmol/liter) and women (mean, 17.6 (SD, 15.0) nmol/l vs. mean, 20.9 (SD, 18.0) nmol/liter).

A significant linear association between the logarithm of serum enterolactone concentration and the number of anti-microbial administrations was observed for both genders (figure 1). Compared with the previous level, each additional antimicrobial treatment lowered serum enterolactone concentration by 16 percent (95 percent confidence interval (CI): 11, 20) in men and 11 percent (95 percent CI: 7, 14) in women.

View larger version (13K): [in this window] [in a new window]   FIGURE 1. Serum enterolactone concentration according to number of antimicrobial treatments, Finland, 1997. Symbols denote the crude mean values and the plotted lines the mean values adjusted for body mass index, occurrence of constipation, consumption of lignan-containing foods, and smoking.

 
A significant trend toward a higher logarithm of serum enterolactone concentration with increasing time from the last antimicrobial treatment was also observed for both genders (figure 2). Compared with the previous level, for each 2-month time period, serum enterolactone concentration increased by 8 percent (95 percent CI: 5, 10) in men and 6 percent (95 percent CI: 3, 8) in women. Serum enterolactone concentration was associated with the number of treatments and the time from the last administration (figure 3). The associations were similar for both men and women, although women had a higher serum enterolactone concentration than men.

View larger version (15K): [in this window] [in a new window]   FIGURE 2. Serum enterolactone concentration according to time (number of months) from the last antimicrobial treatment, Finland, 1997. Symbols denote the crude mean values and the plotted lines the mean values adjusted for body mass index, occurrence of constipation, consumption of lignan-containing foods, and smoking.

 

View larger version (32K): [in this window] [in a new window]   FIGURE 3. Serum enterolactone concentration according to the time (number of months) from the last antimicrobial treatment and the number of treatments, Finland, 1997. Adjusted for body mass index, occurrence of constipation, consumption of lignan-containing foods, and smoking. *, p < 0.05 compared with those who had purchased antimicrobials a maximum (max) of once and with time from treatment being at least 3 months.

 
The most frequently prescribed antimicrobials were cephalosporins (25 percent of the prescriptions), the majority of which consisted of first-generation preparations. The other major groups were tetracyclines (24 percent), macrolides and lincosamides (18 percent), and amoxicillin and other extended-spectrum penicillins (13 percent); the other antimicrobial agents together constituted about 20 percent of the prescriptions. There were modest differences in serum enterolactone concentration between various antimicrobials (figure 4). The strongest suppression in serum enterolactone concentration seemed to be caused by macrolides (10.5 nmol/liter), while phenoxymethylpenicillin and other beta-lactamase-sensitive penicillins (18.3 nmol/liter), cephalosporins (15.6 nmol/liter), and amoxicillin and other extended-spectrum penicillins (15.2 nmol/liter) had minor effects. When only those subjects who had no prior use of antimicrobials were included in the analysis, the impression was still the same, except for amoxicillin and other extended-spectrum penicillins as well as macrolides (17.5 and 12.1 nmol/liter, respectively).

View larger version (22K): [in this window] [in a new window]   FIGURE 4. Serum enterolactone concentration according to type of the last antimicrobial treatment (time from treatment being a maximum of 3 months), Finland, 1997. Adjusted for body mass index, occurrence of constipation, consumption of lignan-containing foods, and smoking.

 

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Serum enterolactone concentration was significantly lower in subjects who had purchased oral antimicrobials up to 12–16 months before serum sampling than in nonusers. Serum enterolactone level was associated with both number of treatments and length of time from the last treatment. Furthermore, modest differences were found between the various antimicrobials. These findings support our view of the crucial role of gut microflora in the metabolism of lignans.

Previously, a small-scale human study showed that oral administration of metronidazole or wide-spectrum oxytetracycline reduces urinary excretion of lignans (17), whereas another study did not find significant differences in enterolactone levels between antimicrobial users and nonusers (25). Our results are consistent with the findings of the first study; we found notably lower serum enterolactone concentrations in subjects who had used antimicrobials than in nonusers. This suppression was similar in both genders and was not affected by consumption of lignan-containing foods, smoking, BMI, or constipation. Furthermore, the lowest serum enterolactone concentrations were found in subjects who had recently used antimicrobials. Thus, the contradictory results obtained for the association between use of antimicrobials and enterolactone concentration may be due to the fact that Horn-Ross et al. (25) had no data on how recently the antimicrobials had been used. After antimicrobial use ceased, serum enterolactone levels seemed to increase over at least a 6–7-month period. However, no obvious plateau occurred, suggesting that it might take even longer for concentrations to be fully restored. Intestinal microflora has been reported to return to its normal level within 2 weeks of administration of antimicrobials (26–28). However, our results suggest that the ability of microflora to metabolize lignans normalizes more slowly. In addition, an inverse association was observed between serum enterolactone concentration and number of antimicrobial prescriptions. This finding is in accordance with some earlier observations showing greater disturbances in the intestinal flora after repeated treatments (29).

By affecting the intestinal flora, antimicrobials presumably interfere with formation of enterolactone from its precursors. Antimicrobials might also interfere with enzymatic hydrolysis of enterolactone conjugates excreted in bile, reducing enterolactone reabsorption (enterohepatic circulation) from the gut. As a result of antibiotic-associated diarrhea, metabolism and absorption of lignans may be incomplete. Other mechanisms, such as stimulation of enterolactone-metabolizing enzymes in the liver, cannot be ruled out, however.

Differences between various antimicrobials regarding serum enterolactone concentration were moderate. Serum enterolactone concentration was strongly suppressed by macrolides, whereas amoxicillin and other extended-spectrum penicillins, phenoxymethylpenicillin and other beta-lactamase-sensitive penicillins, and cephalosporins seemed to have minor effects. This finding is in accordance with earlier studies (30–32) showing that macrolides induce remarkable changes in both the aerobic and anaerobic microflora, while amoxicillin, phenoxymethylpenicillin, and cephalosporins cause minor ecologic alterations. The fact that most differences between various antimicrobials regarding serum enterolactone concentration did not reach statistical significance may be due to subjects using several different types of drugs and the small number of subjects in each drug group. Furthermore, it may reflect individual variation in the effect of antimicrobials on gastrointestinal flora.

Epidemiologic studies demonstrate an elevated risk of breast cancer for women with a low urinary enterolactone level (11) and of acute coronary events for men with a low serum enterolactone concentration (12). This finding raises the question of whether long-term or repeated antimicrobial treatments might lead to prolonged lowering of serum enterolactone concentration, thus enhancing the risk of chronic diseases. Thus far, the causality of these events remains speculative, although a recent study reported an elevated risk of breast cancer for women who had a history of medication use for urinary tract infection (33).

We used a nationwide drug register to obtain data on purchases of antimicrobials. The coverage of this register is very good; at the time of our study, more than 95 percent of Finnish pharmacies were covered. The only pharmacies excluded from the register were those without a computer system for handling prescriptions. We also had no data on antimicrobials received in hospitals. However, only 12 percent of all antimicrobials are used in hospitals (34). Information was also lacking on the dosages of these antimicrobials and the length of treatment, as well as antimicrobials not included in the reimbursement system because of their low price (less than 8 euros (US $8)). Most of these inexpensive drugs are phenoxymethylpenicillin, sulfa-trimethoprim, and nalidixic acid, which have been suggested to have a minor impact on microflora (31, 32). Another limitation is the fact that purchase of antimicrobials does not necessarily mean actual use. However, this possible error would only attenuate the results.

In conclusion, we found that lowered serum enterolactone concentration was associated with use of antimicrobials. This finding is in line with the known role of gut microflora in formation of mammalian lignans from their precursors. Our findings also suggest that recent use of antimicrobials should be considered when the association between serum enterolactone concentration and risk of chronic diseases is studied. The importance of antimicrobials in the prophylaxis and treatment of infections should not be underestimated. However, extended use of antimicrobials and the trend toward broad-spectrum preparations are alarming, especially since a substantial portion of antibiotic use has questionable therapeutic value (35). Besides being expensive, overuse of broad-spectrum antimicrobials may also have implications for increasing antimicrobial resistance and the risk of chronic diseases. To avoid these serious consequences, more attention should be directed at the appropriate use of antimicrobials.

	ACKNOWLEDGMENTS

 
This study was supported by the Finnish Cultural Foundation and the Juha Vainio Foundation.

	NOTES

 
Reprint requests to Annamari Kilkkinen, Department of Epidemiology and Health Promotion, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, Finland (e-mail: annamari.kilkkinen{at}ktl.fi).

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Adlercreutz H, Höckerstedt K, Bannwart C, et al. Effect of dietary components, including lignans and phytoestrogens, on enterohepatic circulation and liver metabolism of estrogens and on sex hormone binding globulin (SHBG). J Steroid Biochem 1987;27:1135–44.[ISI][Medline]
2. Hirano T, Fukuoka K, Oka K, et al. Antiproliferative activity of mammalian lignan derivatives against the human breast carcinoma cell line, ZR-75-1. Cancer Invest 1990;8:595–602.[ISI][Medline]
3. Mousavi Y, Adlercreutz H. Enterolactone and estradiol inhibit each other's proliferative effect on MCF-7 breast cancer cells in culture. J Steroid Biochem Molec Biol 1992;41:615–19.[ISI][Medline]
4. Adlercreutz H, Bannwart C, Wähälä K, et al. Inhibition of human aromatase by mammalian lignans and isoflavonoid phytoestrogens. J Steroid Biochem Mol Biol 1993;44:147–53.[ISI][Medline]
5. Sathyamoorthy N, Wang TT, Phang JM. Stimulation of pS2 expression by diet-derived compounds. Cancer Res 1994;54:957–61.[Abstract/Free Full Text]
6. Evans BAJ, Griffiths K, Morton MS. Inhibition of 5·-reductase in genital skin fibroblast prostate tissue by dietary lignans and isoflavonoids. J Endocrinol 1995;147:295–302.[Abstract]
7. Adlercreutz H, Mazur W. Phyto-oestrogens and western diseases. Ann Med 1997;29:95–120.[ISI][Medline]
8. Wang C, Kurzer MS. Effects of phytoestrogens on DNA synthesis in MCF-7 cells in the presence of estradiol or growth factors. Nutr Cancer 1998;31:90–100.[ISI][Medline]
9. Thompson L, Seidl M, Rickard S, et al. Antitumorigenic effect of a mammalian lignan precursor from flaxseed. Nutr Cancer 1996;26:159–65.[ISI][Medline]
10. Thompson L, Rickard S, Orcheson L, et al. Flaxseed and its lignan and oil component reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis 1996;17:1373–6.[Abstract/Free Full Text]
11. Ingram D, Sanders K, Kolybaba M, et al. Case-control study of phyto-estrogens and breast cancer. Lancet 1997;350:990–4.[ISI][Medline]
12. Vanharanta M, Voutilainen S, Lakka TA, et al. Risk of acute coronary events according to serum concentrations of enterolactone: a prospective population-based case-control study. Lancet 1999;354:2112–15.[ISI][Medline]
13. Mazur W, Fotsis T, Wähälä K, et al. Isotope dilution gas chromatographic-mass spectrometric method for the determination of isoflavonoids coumestrol and lignans in food samples. Anal Biochem 1996;233:169–80.[ISI][Medline]
14. Mazur W. Phytoestrogen content in foods. Baillieres Clin Endocrinol Metab 1998;12:729–42.[ISI][Medline]
15. Thompson LU, Robb P, Serraino M, et al. Mammalian lignan production from various foods. Nutr Cancer 1991;16:43–52.[ISI][Medline]
16. Heinonen S, Nurmi T, Liukkonen K, et al. The occurrence of new mammalian lignan precursors in whole grain. J Agric Food Chem 2001;49:3178–86.[ISI][Medline]
17. Setchell KDR, Lawson AM, Borriello SP, et al. Lignan formation in man—microbial involvement and possible roles in relation to cancer. Lancet 1981;2:4–7.[ISI][Medline]
18. Borriello SP, Setchell KDR, Axelson M, et al. Production and metabolism of lignans by the human faecal flora. J Appl Bacteriol 1985;58:37–43.[Medline]
19. Setchell KDR, Adlercreutz H. Mammalian lignans and phyto-oestrogens: recent studies on their formation, metabolism and biological role in health and disease. In: Rowland IA, ed. The role of gut microflora in toxicity and cancer. New York, NY: Academic Press, 1988:315–45.
20. Kilkkinen A, Stumpf K, Pietinen P, et al. Determinants of serum enterolactone concentration. Am J Clin Nutr 2001;73:1094–100.[Abstract/Free Full Text]
21. FINDIET 1997 Study Group. The 1997 dietary survey of Finnish adults. Helsinki, Finland: National Public Health Institute, 1998:B8.
22. World Health Organization. Collaborating Centre for Drug Statistics Methodology. Guidelines for ATC classification and DDD assignment. Oslo, Norway: World Health Organization, 1998.
23. Adlercreutz H, Wang GJ, Lapcík O, et al. Time-resolved fluoroimmunoassay for plasma enterolactone. Anal Biochem 1998;265:208–15.[ISI][Medline]
24. Stumpf K, Uehara M, Nurmi T, et al. Changes in time-resolved fluoroimmunoassay of plasma enterolactone. Anal Biochem 2000;284:153–7.[ISI][Medline]
25. Horn-Ross PL, Barnes S, Kirk M, et al. Urinary phytoestrogen levels in young women from a multiethnic population. Cancer Epidemiol Biomarkers Prev 1997;6:339–45.[Abstract]
26. Brismar B, Edlund C, Nord CE. Comparative effects of clarithromycin and erythromycin on the normal intestinal microflora. Scand J Infect Dis 1991;23:635–42.[ISI][Medline]
27. Brismar B, Edlund C, Nord CE. Impact of cefpodoxime proxetil and amoxicillin on the normal oral and intestinal microflora. Eur J Clin Microbiol Infect Dis 1993;12:714–19.[ISI][Medline]
28. Eckernäs SÅ, Grahnén A, Nord CE. Impact of dirithromycin on the normal oral and intestinal microflora. Eur J Clin Microbiol Infect Dis 1991;10:688–92.[ISI][Medline]
29. Edlund C, Barkholt L, Olsson-Liljequist B, et al. Effect of vancomycin on intestinal flora of patients who previously received antimicrobial therapy. Clin Infect Dis 1997;25:729–32.[ISI][Medline]
30. Hooker KD, DiPiro JT. Effect of antimicrobial therapy on bowel flora. Clin Pharm 1988;7:878–88.[ISI][Medline]
31. Nord CE, Heimdahl A, Kager L. Antimicrobial induced alterations of the human oropharyngeal and intestinal microflora. Scand J Infect Dis Suppl 1986;49:64–72.[Medline]
32. Nord CE, Edlund C. Impact of antimicrobial agents on human intestinal microflora. J Chemother 1990;2:218–37.[ISI][Medline]
33. Knekt P, Adlercreutz H, Rissanen H, et al. Does antibacterial treatment for urinary tract infection contribute to the risk of breast cancer? Br J Cancer 2000;82:1107–10.[ISI][Medline]
34. National Agency for Medicines and Social Insurance Institution. Finnish statistics on medicines 1998. Helsinki, Finland: National Agency for Medicines and Social Insurance Institution, 1999.
35. Wise R, Hart T, Cars O, et al. Antimicrobial resistance is a major threat to public health. BMJ 1998;317:609–10.[Free Full Text]

Received for publication April 2, 2001. Accepted for publication September 5, 2001.

CiteULike    Connotea    Del.icio.us    What's this?

This article has been cited by other articles:

				M. Hedelin, M. Lof, M. Olsson, H. Adlercreutz, S. Sandin, and E. Weiderpass Dietary Phytoestrogens Are Not Associated with Risk of Overall Breast Cancer But Diets Rich in Coumestrol Are Inversely Associated with Risk of Estrogen Receptor and Progesterone Receptor Negative Breast Tumors in Swedish Women J. Nutr., May 1, 2008; 138(5): 938 - 945. [Abstract] [Full Text] [PDF]

				A. Kuijsten, P. C. H. Hollman, H. C. Boshuizen, M. N. C. P. Buijsman, P. van 't Veer, F. J. Kok, I. C. W. Arts, and H. B. Bueno-de-Mesquita Plasma Enterolignan Concentrations and Colorectal Cancer Risk in a Nested Case-Control Study Am. J. Epidemiol., March 15, 2008; 167(6): 734 - 742. [Abstract] [Full Text] [PDF]

				I. E. J. Milder, A. Kuijsten, I. C. W. Arts, E. J. M. Feskens, E. Kampman, P. C. H. Hollman, and P. Van 't Veer Relation between Plasma Enterodiol and Enterolactone and Dietary Intake of Lignans in a Dutch Endoscopy-Based Population J. Nutr., May 1, 2007; 137(5): 1266 - 1271. [Abstract] [Full Text] [PDF]

				M. R. French, L. U. Thompson, and G. A. Hawker Validation of a Phytoestrogen Food Frequency Questionnaire with Urinary Concentrations of Isoflavones and Lignan Metabolites in Premenopausal Women J. Am. Coll. Nutr., February 1, 2007; 26(1): 76 - 82. [Abstract] [Full Text] [PDF]

				A. Rossini, C. Rumio, L. Sfondrini, E. Tagliabue, D. Morelli, R. Miceli, L. Mariani, M. Palazzo, S. Menard, and A. Balsari Influence of Antibiotic Treatment on Breast Carcinoma Development in Proto-neu Transgenic Mice. Cancer Res., June 15, 2006; 66(12): 6219 - 6224. [Abstract] [Full Text] [PDF]

				A. Kuijsten, I. C.W. Arts, P. C.H. Hollman, P. van't Veer, and E. Kampman Plasma enterolignans are associated with lower colorectal adenoma risk. Cancer Epidemiol. Biomarkers Prev., June 1, 2006; 15(6): 1132 - 1136. [Abstract] [Full Text] [PDF]

				R. Piller, E. Verla-Tebit, S. Wang-Gohrke, J. Linseisen, and J. Chang-Claude CYP17 Genotype Modifies the Association between Lignan Supply and Premenopausal Breast Cancer Risk in Humans J. Nutr., June 1, 2006; 136(6): 1596 - 1603. [Abstract] [Full Text] [PDF]

				A. Kilkkinen, I. Erlund, M. J. Virtanen, G. Alfthan, K. Ariniemi, and J. Virtamo Serum Enterolactone Concentration and the Risk of Coronary Heart Disease in a Case-Cohort Study of Finnish Male Smokers Am. J. Epidemiol., April 15, 2006; 163(8): 687 - 693. [Abstract] [Full Text] [PDF]

				A. Stuedal, I. T. Gram, Y. Bremnes, H. Adlercreutz, M. B. Veierod, and G. Ursin Plasma Levels of Enterolactone and Percentage Mammographic Density among Postmenopausal Women Cancer Epidemiol. Biomarkers Prev., September 1, 2005; 14(9): 2154 - 2159. [Abstract] [Full Text] [PDF]

				A. Kuijsten, I. C. W. Arts, T. B. Vree, and P. C. H. Hollman Pharmacokinetics of Enterolignans in Healthy Men and Women Consuming a Single Dose of Secoisolariciresinol Diglucoside J. Nutr., April 1, 2005; 135(4): 795 - 801. [Abstract] [Full Text] [PDF]

				D. Bhakta, I. dos Santos Silva, C. Higgins, L. Sevak, T. Kassam-Khamis, P. Mangtani, H. Adlercreutz, and A. McMichael A Semiquantitative Food Frequency Questionnaire Is a Valid Indicator of the Usual Intake of Phytoestrogens by South Asian Women in the UK Relative to Multiple 24-h Dietary Recalls and Multiple Plasma Samples J. Nutr., January 1, 2005; 135(1): 116 - 123. [Abstract] [Full Text] [PDF]

				A. Olsen, K. E. B. Knudsen, B. L. Thomsen, S. Loft, C. Stripp, K. Overvad, S. Moller, and A. Tjonneland Plasma Enterolactone and Breast Cancer Incidence by Estrogen Receptor Status Cancer Epidemiol. Biomarkers Prev., December 1, 2004; 13(12): 2084 - 2089. [Abstract] [Full Text] [PDF]

				C. M. Velicer, S. R. Heckbert, J. W. Lampe, J. D. Potter, C. A. Robertson, and S. H. Taplin Antibiotic Use in Relation to the Risk of Breast Cancer JAMA, February 18, 2004; 291(7): 827 - 835. [Abstract] [Full Text] [PDF]

				R. B. Ness and J. A. Cauley Antibiotics and Breast Cancer--What's the Meaning of This? JAMA, February 18, 2004; 291(7): 880 - 881. [Full Text] [PDF]

				A. N. Begum, C. Nicolle, I. Mila, C. Lapierre, K. Nagano, K. Fukushima, S.-M. Heinonen, H. Adlercreutz, C. Remesy, and A. Scalbert Dietary Lignins Are Precursors of Mammalian Lignans in Rats J. Nutr., January 1, 2004; 134(1): 120 - 127. [Abstract] [Full Text] [PDF]

				A. Kilkkinen, J. Virtamo, M. J. Virtanen, H. Adlercreutz, D. Albanes, and P. Pietinen Serum Enterolactone Concentration Is Not Associated with Prostate Cancer Risk in a Nested Case-Control Study Cancer Epidemiol. Biomarkers Prev., November 1, 2003; 12(11): 1209 - 1212. [Abstract] [Full Text]

				R. M. Blair, S. E. Appt, A. A. Franke, and T. B. Clarkson Treatment with Antibiotics Reduces Plasma Equol Concentration in Cynomolgus Monkeys (Macaca fascicularis) J. Nutr., July 1, 2003; 133(7): 2262 - 2267. [Abstract] [Full Text] [PDF]

				A. Kilkkinen, L. M. Valsta, J. Virtamo, K. Stumpf, H. Adlercreutz, and P. Pietinen Intake of Lignans Is Associated with Serum Enterolactone Concentration in Finnish Men and Women J. Nutr., June 1, 2003; 133(6): 1830 - 1833. [Abstract] [Full Text] [PDF]

				M. Vanharanta, S. Voutilainen, T. H. Rissanen, H. Adlercreutz, and J. T. Salonen Risk of Cardiovascular Disease-Related and All-Cause Death According to Serum Concentrations of Enterolactone: Kuopio Ischaemic Heart Disease Risk Factor Study Arch Intern Med, May 12, 2003; 163(9): 1099 - 1104. [Abstract] [Full Text] [PDF]

				K. E. Bach Knudsen, A. Serena, A. K. B. Kjaer, I. Tetens, S.-M. Heinonen, T. Nurmi, and H. Adlercreutz Rye Bread in the Diet of Pigs Enhances the Formation of Enterolactone and Increases Its Levels in Plasma, Urine and Feces J. Nutr., May 1, 2003; 133(5): 1368 - 1375. [Abstract] [Full Text] [PDF]

				K. Stumpf and H. Adlercreutz Short-Term Variations in Enterolactone in Serum, 24-Hour Urine, and Spot Urine and Relationship with Enterolactone Concentrations Clin. Chem., January 1, 2003; 49(1): 178 - 181. [Full Text] [PDF]

				P. Huovinen Macrolide-Resistant Group A Streptococcus -- Now in the United States N. Engl. J. Med., April 18, 2002; 346(16): 1243 - 1245. [Full Text] [PDF]

				Enterolactones, Intestinal Microflora, and Antibiotics Journal Watch Infectious Diseases, April 11, 2002; 2002(411): 10 - 10. [Full Text]

This Article Abstract FREE Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (54)