Abstract
Objective
To evaluate exposure to tobacco, marijuana and indoor heating/cooking sources in relation to anti-Müllerian hormone (AMH) levels.
Design
Cross-sectional analysis in a sample of premenopausal women (N=913) enrolled in the Sister Study cohort (n=50,884).
Setting
U.S. adult sample
Patient(s)
Women, 35–54 at time of enrollment, with an archived serum sample, at least 1 intact ovary, and classified as premenopausal.
Intervention(s)
Not applicable
Main Outcome Measures
Serum AMH (ng/ml) levels ascertained by ultrasensitive ELISA assay
Results
Lower AMH levels were associated with sources of indoor heating, including burning wood (−36.0%, 95%CI:−55.7, −7.8%) or artificial firelogs (−45.8%, 95%CI:−67.2, −10.4) at least 10 times/year in a residential indoor stove/fireplace. Lower AMH levels were also observed in women who were current smokers of ≥20 cigarettes/day relative to non-smokers (−56.2%, 95%CI:−80.3, −2.8%) and in women with 10+ years of adult environmental tobacco smoke (ETS) exposure (−31.3%, 95%CI:−51.3, −3.1%) but no associations were observed for marijuana use.
Conclusions
We confirmed previously reported findings of lower AMH levels in current heavy smokers and also found associations for long-term ETS exposure and indoor burning of wood or artificial firelogs. These findings suggest that combustion by-products from common exposures can have toxic effects on the human ovary.
Keywords: tobacco, environmental tobacco smoke, Anti-Müllerian Hormone, breast cancer, indoor air pollution, indoor heating/cooking
Introduction
The potential impact of the environment and lifestyle factors on reproductive health is of concern to many women. Anti-Müllerian Hormone (AMH) is a marker of ovarian reserve, as serum AMH levels reflect the ovarian follicular pool (1). Ovarian reserve testing can provide information to inform fertility-related clinical treatment decisions; for example, AMH correlates with IVF success rates (2). Additionally, higher AMH levels have been associated with increasing time to menopause (3) and breast cancer risk (4, 5).
AMH levels vary by age (6–8) and may be associated with reproductive history (including age at menarche, parity and oral contraceptive use) (7, 9, 10), ethnicity (11), socioeconomic status (10) and polycystic ovarian syndrome (12). Epidemiologic and clinical studies suggest that reproductive health, as measured by AMH, may also be impacted by other environmental exposures, such as radiation and smoking (13, 14). A recent study reported a negative association between self-reported indoor residual spraying (application of pesticides to the inside of dwellings) with pyrethroids and AMH levels in South Africa (15).
Several studies have examined cigarette smoking in relation to AMH levels with inconsistent results (6, 8, 9, 16–22). Although some studies have reported that smoking was associated with lower AMH levels (16, 17, 19–21), other studies have not observed this (6, 8, 9, 18, 22). However, many of these studies have been limited by not considering duration or frequency of tobacco use. Few studies have considered the potential role of environmental tobacco smoke (ETS) (19). One previous study considered household air pollution from the use of indoor cook stoves in women 20–30 years of age, but did not find an association with AMH levels (15). Cigarette smoking, marijuana use and burning fuel for heating and cooking in the home all result in exposure to similar combustion by-products including polycyclic aromatic hydrocarbons (PAH) (23, 24). Benzo[a]pyrene, a commonly measured PAH which is often used in experimental studies, has been previously found to decrease AMH levels in mice (25), and thus these related exposures may be relevant to human populations as well.
In this study, we aimed to evaluate associations between AMH levels, a marker of ovarian reserve, and cigarette and marijuana smoking history, ETS exposure and indoor heating and cooking fuel sources in a sample of premenopausal women enrolled in the Sister Study cohort.
Materials and Methods
Parent Study
The National Institute of Environmental Health Sciences (NIEHS) Sister Study prospective cohort was designed to evaluate genetic and environmental risk factors for breast cancer. During 2003–2009, 50,884 women in the U.S. and Puerto Rico were recruited using a multi-media campaign and a network of volunteers, breast cancer professionals, and advocates. Eligible women were ages 35–74 and had a sister who had been diagnosed with breast cancer but did not have a history of breast cancer themselves.
At enrollment, study participants completed baseline questionnaires on demographics, medical and family history, and lifestyle factors including history of tobacco exposure, marijuana use and indoor heating and cooking. Trained phlebotomists collected blood samples during a home visit at study enrollment. Blood samples were shipped overnight to the Sister Study laboratory. Serum was isolated and samples were stored in liquid nitrogen.
Ethical Approval
This research was approved by the Institutional Review Boards of the National Institute of Environmental Health Sciences, NIH, and the Copernicus Group. Written informed consent was obtained from all participants. Data presented here were from the Sister Study data release 4.0 (May 2015).
Study design
Women selected for this analysis participated as controls in a nested case-control study of AMH and breast cancer risk that has been previously described (4). Briefly, to be eligible for selection in to the case-control study, Sister Study participants were required to be ages 35–54 at time of enrollment, have an archived serum sample, at least 1 intact ovary, and be categorized as premenopausal (4). Premenopausal status was defined as reporting at least one menstrual cycle in the 12 months prior to study enrollment. If women had a hysterectomy without bilateral oophorectomy they were characterized as being premenopausal. Only the controls, women without breast cancer as of December 31, 2012, were included in the analysis presented here. Samples for 916 controls were analyzed for AMH levels and 3 samples were excluded due to prior prophylactic bilateral mastectomy or low quality samples. The final sample size included 913 controls.
Exposure Assessment
As part of the baseline questionnaire, women were asked about their use of tobacco cigarettes, marijuana, exposure to cigarette smoke from other people and indoor heating and cooking practices. Smoking was defined as smoking at least one cigarette per day for six months or longer. All women were asked the ages they started and stopped smoking and the number of cigarettes per day/week/month they smoked. Women were categorized as being nonsmokers, past smokers or current smokers. Age started smoking (nonsmokers, < 15 years, 15–19 years, 20+ years), total pack-years (nonsmokers, <5, 5–14, 15+), total years (nonsmokers, <10 years, 10+ years) and time since smoking (nonsmokers, <15 years, 15+ years) were considered. Marijuana smoking history was defined as ever smoking marijuana and women were categorized as never, past or current marijuana smokers. Frequency (never smoked, less than twice a month, more than twice a month), age started (never smoked, < 15 years, 15–19 years, 20+ years) and total years of marijuana use (never smoked, <2 years, 2–4 years, 5–9 years, 10+ years) were also considered.
Women were classified as ETS exposed if they reported that someone smoked at least 1 cigarette per day in their presence for at least 6 months. ETS exposure was evaluated for childhood and adolescence (defined as exposures occurring prior to 18 years of age) and adult time periods. Total years of ETS (none, 0–9, 10–19, 20+), years of adult ETS (none, 0–9, 10+) and years of childhood/adolescent ETS (none, 0–9, 10–17, 18) were characterized. We also considered a combined adult and childhood/adolescent ETS exposure variable (low childhood/low adult, high childhood/low adult, low childhood/high adult, high childhood/high adult) where childhood (<18 years, 18 years) and adult ETS (<8 years, 8+ years) were dichotomized at the median. Additional ETS variables were also considered, including (1) using a combined active smoking/ETS variable (no active nor ETS, ETS only, active only, active and ETS) with both adult and childhood/adolescent ETS and (2) evaluating early childhood (<12 years) and adolescent ETS (12+ years) separately.
Women were asked whether their mother or anyone else in the household smoked while she was pregnant with them and whether their biological father smoked in the three months prior to conception with the following possible responses: definitely not, probably not, probably did, definitely. Probably not and probably did were collapsed into an unsure category for the following final categories: definitely not, unsure, definitely. All ETS exposures described above were also considered in analyses limited to nonsmoking women (n=561).
To assess indoor heating and cooking exposure, women were asked about the type of heating and cooking fuel in the adult residence that they lived the longest. Information on the energy source for the stove top (electricity, gas, propane), whether or not they used a fireplace or indoor wood-burning stove in the home, what fuel they tended to burn in the fireplace/stove (wood, natural gas/propane, artificial firelogs) and how often (never, ≤10 times/year, >10 times/year) was evaluated.
Laboratory assays
AMH assays were performed at the Reproductive Endocrine Research Laboratory at the University of Southern California Keck School of Medicine. AMH was measured primarily using an Ultrasensitive AMH ELISA kit (Ansh Labs, Webster, TX). However, when AMH levels were below the limit of detection of the Ultrasensitive ELISA (<0.07 ng/ml), the picoAMH ELISA kit (Ansh Labs) was used and recovered levels for 83 control samples. The limit of detection of the picoAMH ELISA is 0.003 ng/ml.
Statistical analysis
Serum AMH levels were skewed with a long tail to the right. Therefore, log-transformed values were calculated to approximate a normal distribution for analysis of AMH concentration as a continuous variable. AMH samples that fell below the LOD (27%) were imputed as the mean of random samples below the LOD, drawn from a lognormal distribution based on the mean and standard deviation of the original AMH sample (26).
We estimated age- and multivariable-adjusted differences in geometric mean AMH in association with tobacco use, marijuana use, ETS and indoor heating and cooking exposures using linear regression and calculated average percent change using the formula [[exp(β)−1] × 100].
Two different adjustment sets were used to control for confounding and covariates were selected a priori. For adult active tobacco and marijuana smoking, ETS and indoor heating and cooking, estimates were adjusted for age (continuous), combined parity and breastfeeding history (nulliparous, parous and never breastfed, parous and breastfed), race (non-Hispanic white, other), education (high school/general education diploma (GED) or less, some college/associate or technical degree, college graduate or more) and household income in the previous year (<$49,999, $50,000–$99,999, $100,000+). For in utero and childhood exposures, including ETS exposure and age started smoking cigarettes or marijuana, multivariable models adjusted for the following covariates: age (continuous), race (non-Hispanic white, other), maternal education (did not complete high school, completed high school/GED, some college or more) and childhood household income (well off, middle income, low income, poor).
Sensitivity Analyses
A sensitivity analysis was done excluding those who were currently using any hormonal birth control [n=81 (9%)] or had undergone unilateral oophorectomy [n=45 (6%)] from all analyses. Smoking may result in earlier age at menopause (27), therefore older smokers who have already gone through menopause may have been selectively excluded from our sample of premenopausal women. Thus, we also conducted a sensitivity analysis repeating the smoking and ETS analyses limiting to women who were ≤48 years at the time of blood draw [n=504 (55%)]. In addition, we tested for differences in the age-related decline of AMH for this subset of women. A longitudinal study of age-related decline of AMH in late-reproductive-age women showed a steeper decline in AMH with age for smokers than for nonsmokers i.e., the difference in AMH between smokers and non-smokers increased significantly with age (28). We can test for differences in the age-related decline in AMH in our cross-sectional data by including a cross-product term, age-by-smoking, rather than the smoking variable as a main effect (21). We conducted this analysis for the active smoking and ETS exposure variables that had at least 15 women in each category. We also conducted the analyses for marijuana use and indoor heating and cooking further adjusted for adult ETS and pack-years of smoking.
All statistical analyses were performed with SAS 9.3 (SAS Institute, Inc., Cary, NC).
Results
Participant characteristics have been previously published (4). Briefly, average age at enrollment was 46.8 (range 35–54), over 90% of women were not using oral contraceptives, women were predominately parous (78%) and almost half had a normal BMI (18.5–24.9 kg/m2) (4). Mean AMH levels were 1.05 ng/mL.
Few women were current smokers (8.4%). The data from the full sample suggest that among all current and past smoking variables, only current heavy smoking (20+ cigarettes/day) was associated with reduced AMH (−55.3%, 95% CI:−79.8, −0.9) (Table I). However, when limiting the sample to women who are 48 years and younger, both heavy smoking (−71.4%, 95% CI:−87.9, −32.4) and high pack-years (−63.4%, 95% CI:−83.5, −18.7) was associated with reduced AMH in current smokers (Supplemental Table I). When the age-specific decline in AMH was examined (by testing an age-by-smoking interaction), heavy current smokers, but not past smokers, showed significantly steeper age-specific declines in AMH compared to never smokers (Supplemental Table II).
Table 1.
Active tobacco smoking and adjusted percent changes in anti-Müllerian hormone (AMH) levels, Sister Study
| Cigarette Smoking History | N | % | Age adjusted % change and 95%CI | Multivariable adjusted % change and 95% CI a,b | |
|---|---|---|---|---|---|
| Cigarette smoking status | |||||
| Nonsmokers | 561 | 61.5 | 0.0 (referent) | 0.0 (referent) | |
| Current Smokers | 77 | 8.4 | −27.0 (−30.2, 24.5) | −4.3 (−28.8, 28.6) | |
| Past smoker | 275 | 30.1 | −6.8 (−30.2, 24.5) | −13.7 (−47.8, 42.5) | |
| Current Smokers versus Never Smokers | |||||
| Age started smoking | |||||
| Nonsmokers | 561 | 87.9 | 0.0 (referent) | 0.0 (referent) | |
| <15 | 18 | 2.8 | −45.7 (−78.0, 34.3) | −44.6 (−79.2, 47.4) | |
| 15–19 | 43 | 6.7 | −38.6 (−66.2, 11.8) | −34.8 (−64.5, 19.6) | |
| 20+ | 16 | 2.5 | 63.6 (−37.2, 326.1) | 64.7 (−38.4, 339.9) | |
| Cigarettes/day usual | |||||
| Nonsmokers | 561 | 87.9 | 0.0 (referent) | 0.0 (referent) | |
| <10 cig/day | 27 | 4.2 | 60.2 (−23.9, 237.4) | 89.6 (−10.5, 301.7) | |
| 10–19 cigs/day | 24 | 3.8 | −43.8 (−74.4, 23.2) | −21.9 (−66.1, 80.3) | |
| 20+ cigs/day | 26 | 4.1 | −58.4 (−80.4, −11.4) | −55.3 (−79.8, −0.9) | |
| Total pack-years | |||||
| Nonsmokers | 561 | 88.1 | 0.0 (referent) | 0.0 (referent) | |
| <5 | 16 | 2.5 | 47.4 (−43.5, 284.7) | 78.2 (−31.9, 366.6) | |
| 5 to 14 | 22 | 3.5 | −12.1 (−61.5, 100.4) | 24.0 (−47.7, 194.1) | |
| 15+ | 38 | 6.0 | −51.0 (−74.0, −7.6) | −44.2 (−71.6, 9.4) | |
| Total years smoked cigarettes | |||||
| Nonsmokers | 561 | 88.1 | 0.0 (referent) | 0.0 (referent) | |
| <10 years | 9 | 1.4 | 14.4 (−68.1, 309.3) | 38.7 (−61.5, 399.3) | |
| 10+ years | 67 | 10.5 | −31.2 (−57.8, 12.4) | −13.9 (−49.2, 45.9) | |
| Past Smokers versus Never Smokers | |||||
| Age started smoking | |||||
| Nonsmokers | 561 | 67.1 | 0.0 (referent) | 0.0 (referent) | |
| <15 years | 49 | 5.9 | 22.1 (−31.8, 118.7) | 25.3 (−30.6, 126.1) | |
| 15–19 years | 179 | 21.4 | −13.0 (−38.0, 22.1) | −9.5 (−36.0, 28.0) | |
| 20+ years | 47 | 5.6 | −9.8 (−50.3, 63.7) | −4.8 (−47.3, 72.3) | |
| Total pack-years | |||||
| Nonsmokers | 561 | 67.1 | 0.0 (referent) | 0.0 (referent) | |
| <5 | 143 | 17.1 | 5.5 (−26.9, 52.3) | 4.6 (−27.8, 51.6) | |
| 5 to 14 | 82 | 9.8 | −30.9 (−56.6, 9.8) | −27.1 (−54.7, 17.2) | |
| 15+ | 50 | 6.0 | 6.3 (−40.6, 90.0) | 15.7 (−36.1, 109.2) | |
| Total years smoked cigarettes | |||||
| Nonsmokers | 561 | 67.1 | 0.0 (referent) | 0.0 (referent) | |
| <10 | 149 | 17.8 | 3.6 (−27.9, 48.8) | 2.4 (−29.1, 47.8) | |
| 10+ years | 126 | 15.1 | −18.0 (−44.4, 20.9) | −11.7 (−40.7, 31.6) | |
| Time since smoking | |||||
| Nonsmokers | 561 | 67.1 | 0.0 (referent) | 0.0 (referent) | |
| <15 years | 38 | 4.6 | 21.9 (−36.7, 134.9) | 32.4 (−31.8, 157.3) | |
| 15+ years | 237 | 28.4 | −10.9 (−34.4, 21.0) | −9.1 (−33.5, 24.2) | |
Associations for cigarette smoking, total tobacco pack-years, total years of tobacco, time since tobacco smoking, total years and cigarettes/day were adjusted for age, parity, breastfeeding history, race, education and annual household income.
Associations for age started smoking were adjusted for age (continuous), race (non-Hispanic white, other), maternal education (did not complete high school, completed high school/GED, some college or more) and childhood household income (well off, middle income, low income, poor)
There were very few current marijuana users (<1%) (Table II). Marijuana smoking status, frequency, years of use and age of initiation were not associated with AMH levels. Results remained similar with further adjustment for pack-years of smoking and years of adult ETS (data not shown).
Table 2.
Active marijuana smoking and adjusted percent changes in anti-Müllerian hormone (AMH) levels, Sister Study
| Marijuana Smoking History | N | % | Age adjusted % change and 95%CI | Multivariable adjusted % change and 95% CI a,b | |
|---|---|---|---|---|---|
| Marijuana smoking status | |||||
| Never smoked | 320 | 37.6 | 0.0 (referent) | 0.0 (referent) | |
| Past | 525 | 61.6 | 6.0 (−19.7, 39.9) | 2.9 (−22.6, 36.8) | |
| Current | 7 | 0.8 | −68.9 (−93.0, 38.8) | −67.1 (−92.6, 47.3) | |
| Marijuana frequency | |||||
| Never smoked | 320 | 43.0 | 0.0 (referent) | 0.0 (referent) | |
| Less than about twice a month | 241 | 32.4 | 18.6 (−15.3, 66.1) | 9.2 (−22.6, 54.0) | |
| More than about twice a month | 183 | 24.6 | −12.9 (−39.6, 25.6) | −10.7 (−38.5, 29.7) | |
| Age started using marijuana | |||||
| Never smoked | 320 | 37.4 | 0.0 (referent) | 0.0 (referent) | |
| <15 years | 85 | 9.9 | 26.0 (−22.3, 104.4) | 26.1 (−23.9, 108.9) | |
| 15–19 years | 337 | 39.4 | 8.7 (−19.9, 47.6) | 5.4 (−23.0, 44.3) | |
| 20+ years | 113 | 13.2 | −20.1 (−48.0, 22.8) | −17.9 (−46.7, 26.4) | |
| Total years of marijuana use | |||||
| Never smoked | 320 | 37.4 | 0.0 (referent) | 0.0 (referent) | |
| <2 | 238 | 27.8 | −5.2 (−32.3, 32.6) | −9.2 (−35.5, 27.9) | |
| 2 to 4 | 138 | 16.1 | 13.7 (−23.7, 69.4) | 10.9 (−26.2, 66.4) | |
| 5 to 9 | 73 | 8.5 | 32.9 (−20.0, 121.0) | 27.3 (−23.8, 112.5) | |
| 10+ | 86 | 10.1 | −4.4 (−40.6, 53.9) | −4.4 (−40.9, 54.5) | |
Associations for marijuana smoking status, frequency and total years were adjusted for age, parity, breastfeeding history, race, education annual household income.
Associations for age started smoking marijuana were adjusted for age (continuous), race (non-Hispanic white, other), maternal education (did not complete high school, completed high school/GED, some college or more) and childhood household income (well off, middle income, low income, poor)
The ETS exposure data on the full sample (Table III) indicated that 10+ years of adult ETS is associated with reduced AMH (−31.9%, 95% CI:−51.7, −3.9), but there was little or no association for childhood or prenatal exposure. There was a suggestion of reduced AMH associated with paternal smoking during the 3 months prior to pregnancy (Table III). When the sample was limited to women 48 years and younger (Supplemental Table III), 10+ years of adult ETS exposure remains important, but there was no longer a suggestion of adverse effects of paternal smoking during the 3 months prior to pregnancy. There was also a steeper age-specific decline in AMH for participants with 10+ years of adult ETS exposure compared to those without ETS exposure, but no differences for childhood ETS, prenatal exposure, or paternal smoking during the 3 months prior to pregnancy (Supplemental Table IV).
Table 3.
Environmental tobacco smoke (ETS) and adjusted percent changes in anti-Müllerian hormone (AMH) levels, Sister Study
| Environmental Tobacco Smoke (ETS) | N | % | Age adjusted % change and 95%CI | Multivariable adjusted % change and 95% CI a,b | |
|---|---|---|---|---|---|
| Total years of ETS | |||||
| None | 164 | 18.3 | 0.0 (referent) | 0.0 (referent) | |
| 0–9 | 138 | 15.4 | 9.2 (−30.5, 71.6) | 13.0 (−28.6, 78.8) | |
| 10 to 19 | 285 | 31.7 | 1.8 (−30.6, 49.54) | 10.0 (−25.8, 63.0) | |
| 20+ | 311 | 34.6 | −12.1 (−39.9, 28.4) | −3.5 (−35.1, 43.5) | |
| Adult ETS | |||||
| No | 411 | 45.2 | 0.0 (referent) | 0.0 (referent) | |
| Yes | 498 | 54.8 | −26.4 (−43.3, −4.5) | −21.0 (−39.6, 3.4) | |
| Years of adult ETS | |||||
| None | 411 | 45.0 | 0.0 (referent) | 0.0 (referent) | |
| 0–9 | 269 | 29.6 | −16.1 (−38.1, 13.9) | −12.2 (−35.5, 19.6) | |
| 10+ | 229 | 25.1 | −37.1 (−54.4, −13.1) | −31.9 (−51.7, −3.9) | |
| Childhood ETS | |||||
| No | 264 | 29.3 | 0.0 (referent) | 0.0 (referent) | |
| Yes | 637 | 70.7 | 12.6 (−15.5, 50.0) | 10.5 (−17.6, 48.0) | |
| Years of childhood ETS | |||||
| None | 264 | 29.0 | 0.0 (referent) | 0.0 (referent) | |
| 0–9 | 115 | 12.8 | 39.0 (−10.3, 115.2) | 38.7 (−11.4, 117.0) | |
| 10 to 17 | 170 | 18.9 | 20.7 (−17.9, 77.5) | 19.3 (−19.5, 76.8) | |
| 18 | 352 | 39.1 | 1.5 (−26.2, 39.7) | −1.1 (−28.5, 36.8) | |
| Combined adult/child ETS | |||||
| low childhood, low adult | 422 | 46.2 | 0.0 (referent) | 0.0 (referent) | |
| high childhood, low adult | 220 | 24.1 | −2.4 (−29.4, 34.9) | −7.4 (−33.3, 28.6) | |
| low childhood, high adult | 139 | 15.2 | −31.5 (−53.2, 0.3) | −31.3 (−53.4, 1.3) | |
| high childhood, high adult | 132 | 14.5 | −41.0 (−60.0, −12.8) | −39.6 (−59.3, −10.3) | |
| Maternal smoking during pregnancy | |||||
| Definitely Not | 491 | 57.0 | 0.0 (referent) | 0.0 (referent) | |
| Unsure | 129 | 15.0 | 30.9 (−11.3, 93.0) | 34.6 (−9.1, 99.3) | |
| Definitely | 241 | 28.0 | −4.5 (−29.7, 29.8) | −7.4 (−32.2, 26.4) | |
| Paternal Smoking, 3 months prior to pregnancy | |||||
| Definitely Not | 258 | 30.0 | 0.0 (referent) | 0.0 (referent) | |
| Unsure | 140 | 16.3 | −4.0 (−36.5, 45.2) | −8.1 (−39.7, 39.9) | |
| Definitely | 461 | 53.7 | −20.5 (−41.5, 7.9) | −21.2 (−42.3, 7.5) | |
| Anyone in household smoke during pregnancy | |||||
| Definitely Not | 305 | 35.5 | 0.0 (referent) | 0.0 (referent) | |
| Unsure | 159 | 18.5 | −17.0 (−443.5, 21.8) | −22.6 (−47.7, 14.4) | |
| Definitely | 395 | 46.0 | −20.0 (−40.7, 7.9) | −23.3 (−43.3, 3.9) | |
Associations for total years of ETS, adult ETS, and years of adult ETS were adjusted for age, parity, breastfeeding history, race, education and annual household income.
Associations for childhood ETS, years of childhood ETS, maternal smoking during pregnancy, paternal smoking 3 months prior and anyone smoking in the household were adjusted for age, race, maternal education and childhood household income
We did not note any new associations when considering a combined active smoking/ETS variable or when dividing childhood ETS into early childhood and adolescence (data not shown). Nor did limiting the analysis to women who were nonsmokers substantially alter results for ETS (data not shown), and therefore results are presented for all women.
Women who burned wood (−32.5, 95% CI:−51.1, −6.8) or artificial firelogs (−31.6, 95% CI:−54.2, 2.3) in their indoor stove/fireplace had approximately 30% lower AMH levels (Table IV). These associations were more pronounced in women who used their indoor stove/fireplace more than 10 times per year for burning wood (−36.0, 95% CI:−55.7, −7.8) or artificial firelogs (−45.8, 95% CI:−67.2, −10.4) compared to those without an indoor stove/fireplace. No associations with AMH levels were observed for burning natural gas/propane or for the energy sources of the cooking stove top. Results for exposure to indoor heating and cooking sources remained unchanged after further adjustment for pack-years of smoking and years of adult ETS (data not shown).
Table 4.
Indoor air pollution in longest adult residence and adjusted percent changes in anti-Müllerian hormone (AMH) levels, Sister Study
| Indoor air pollution | N | % | Age adjusted % change and 95%CI | Multivariable adjusted % change and 95% CI a | |
|---|---|---|---|---|---|
| Energy source for the cooking stove top | |||||
| Electricity | 545 | 61.8 | 0.0 (referent) | 0.0 (referent) | |
| Gas | 309 | 35.0 | 15.1 (−12.9, 52.1) | 17.9 (−11.1, 56.4) | |
| Propane | 28 | 3.2 | 89.6 (−11.2, 305.4) | 113.1 (−0.5, 356.1) | |
| Stove/fireplace fuel | |||||
| No stove/fireplace | 341 | 44.4 | 0.0 (referent) | 0.0 (referent) | |
| Wood | 319 | 41.5 | −25.5 (−45.3, 1.3) | −32.5 (−51.1, −6.8) | |
| Natural gas or propane | 120 | 15.6 | 11.0 (−27.0, 68.8) | −2.5 (−37.1, 51.1) | |
| Artificial firelogs | 153 | 19.9 | −24.9 (−48.9, 10.4) | −31.6 (−54.2, 2.3) | |
| Wood | |||||
| No stove/fireplace | 341 | 51.7 | 0.0 (referent) | 0.0 (referent) | |
| ≤10 times/year | 118 | 17.9 | −17.3 (−46.0, 26.7) | −27.9 (−53.9, 12.7) | |
| >10 times/year | 201 | 30.5 | −29.7 (−50.7, 0.4) | −36.0 (−55.7, −7.8) | |
| Natural gas/propane | |||||
| No stove/fireplace | 341 | 74.0 | 0.0 (referent) | 0.0 (referent) | |
| ≤10 times/year | 41 | 8.9 | 57.3 (−17.9, 201.2) | 30.1 (−33.4, 154.0) | |
| >10 times/year | 79 | 17.1 | −8.0 (−43.7, 50.3) | −19.0 (−51.6, 35.6) | |
| Artificial firelogs | |||||
| No stove/fireplace | 341 | 69.0 | 0.0 (referent) | 0.0 (referent) | |
| ≤10 times/year | 69 | 14.0 | −5.9 (−44.2, 58.9) | −13.1 (−49.5, 49.5) | |
| >10 times/year | 84 | 17.0 | −37.6 (−61.5, 1.1) | −45.8 (−67.2, −10.4) | |
Adjusted for age, body mass index, parity, breastfeeding history, race, education and annual household income.
Results for active tobacco and marijuana use, ETS exposure and exposure to indoor heating with AMH were similar when women currently using hormonal contraceptives or those who had had a unilateral oophorectomy were excluded (data not shown).
Discussion
In this large, U.S.-based investigation of PAH-related environmental exposures and AMH levels, those who burned wood or artificial firelogs in their indoor stove or fireplace had lower AMH levels relative to those that did not use an indoor stove or fireplace. Similarly, we report lower levels of AMH and/or a steeper age-specific decline in AMH in women who were heavy current smokers or who were exposed to ETS during adulthood. Results presented here are consistent with observations from laboratory studies that report PAH-treated mice have lower AMH levels (25). These PAH-related exposures were all associated with lower AMH, an important biomarker of ovarian function.
Although burning solid fuels for heating and cooking is more common in Africa and Southeast Asia, burning solid fuels remains the primary heat source for over 6 million U.S. citizens (29, 30). Burning wood indoors has been associated with respiratory problems and cancer of the lung and upper aerodigestive tract (31). Burning wood and artificial firelogs releases a number of pollutants, including polychlorinated dibenzodiozins and dibenzofurans, polychlorinated biphenyls, hexachlorobenzene, particulate matter and PAHs (24). Few studies have considered the impact of household air pollution on reproductive outcomes. One previous study of South African women found no association between AMH levels and self-reported indoor cooking over wood fires (15). However, this study did not consider artificial firelogs, which are manufactured logs composed of pressed sawdust and wax. This South African study population differs substantially from the U.S.-based population described here in terms of age, race, socioeconomic status and other environmental exposures that may be relevant to AMH.
Timing of exposure may be a very important consideration for environmental predictors of AMH. In particular, maternal exposures may be relevant to the primordial ovarian follicular pool as it is established in utero (32). About 7 million ovarian follicles are present at 18 weeks of gestation, but by the time of full-term birth, the number of follicles declines to approximately 1 million (33). Laboratory evidence suggests that in utero exposures may be particularly relevant to AMH levels (34). However, the data for humans is very mixed. The Avon Longitudinal Study of Parents and Children (ALSPAC) found paternal, but not maternal, smoking prior to and during pregnancy to be associated with lower AMH levels in adolescent females (ages 14–16) (33). A smaller study of young women (n=279), ages 18–24, conducted in the Netherlands, found higher AMH for maternal smoking after adjusting for socioeconomic status, broadly defined as education level (low, medium, high)(10). Our findings are consistent with two other studies that did not find in utero exposure to ETS to impact adult AMH levels in women, though neither of those adjusted for socioeconomic status, we were able to do this, and still found no association.
Adult ETS exposure was associated with lower AMH levels in this study population. Few previous studies have considered adult ETS exposure with respect to AMH levels and the two that did found no association with AMH (15, 19). Though active smoking is usually considered a greater health risk than ETS, there are different levels of the various compounds in sidestream compared to mainstream smoke. For example, PAHs have been detected at approximately 10-fold higher levels in sidestream compared to mainstream smoke (35). The specific mixture may influence the pathological pathways involved with different health outcomes.
Little to no association was seen between AMH levels and marijuana. However, we had very few current or very frequent marijuana users in our study population and this may have made it difficult to detect an association. To our knowledge, this is the first study to consider the associations between childhood ETS exposure and marijuana smoking (which largely takes place during youth – almost half of our study population began smoking marijuana prior to age 20 years) and AMH levels. Previous research supporting associations between AMH levels and early life factors, such as birth weight (36) and age at menarche (37) underscore the need for further study considering childhood and adolescent exposures.
The existing evidence on AMH and active smoking is inconsistent. Some studies report associations with lower AMH (16, 17, 19–21) and some do not (6, 8, 9, 18, 22). Most prior studies have dichotomized tobacco smoking as ever/never or categorized as current/former/never. A strength of our analysis is the inclusion of timing, duration, intensity and time since quitting in the tobacco smoke exposure assessment. Because smokers have a younger age at menopause on average (27) and our sample of premenopausal women is likely missing older smokers who have already gone through menopause, we evaluated smoking and ETS associations in a subsample of younger women. For this sensitivity analysis, we limited the sample to women who were ≤48 years at blood draw. With this cutpoint we had a large enough sample for meaningful analyses, but all remaining women were at least a few years younger than the average age at menopause (51 years) (38). In this subgroup, we found that the associations with AMH for current smoking were generally stronger. Because the decline in AMH with age accelerates during the years before menopause (28), we also examined the age-specific decline in AMH in this subgroup when sample size allowed. In our data, current smokers showed a faster decline compared to non-smokers.
This study has limitations. Despite being one of the largest investigations to date, a larger sample with greater statistical power may have allowed us to make stronger conclusions about some of the environmental exposures that had modest associations, but included the null value in the confidence interval. The exposure assessments relied on self-report from the study participants and there may have been measurement error particularly when exposures were in the distant past. We also did not have information available on intensity, duration or timing of maternal smoking while pregnant, which may be relevant. While it is possible that smoking history, especially marijuana use, may be misreported, previous studies have found self-reported active smoking of tobacco to be a valid measurement (39). Although many of the questionnaire responses were used to ascertain historic exposure, this study was cross-sectional in design. Additional information may be obtained from the use of longitudinal data.
This study has many strengths. We were able to consider a wide range of related exposures and in particular, some novel exposures including artificial firelogs, marijuana use and childhood ETS exposure. We were also able to adjust for childhood socioeconomic status, which is likely an important factor for early life exposures such as maternal smoking during pregnancy and childhood ETS. The large sample size of this nested study within the Sister Study cohort also allowed us to consider duration of exposure. Much of the existing research on predictors of AMH levels has been conducted outside of the U.S. or among women who visit fertility clinics (12, 20, 22). This study population is likely more generalizable than women who are visiting fertility clinics and may be experiencing trouble conceiving. The findings of this investigation may also be generalizable to women outside of the U.S. as both tobacco use and use of an indoor stove/fireplace for heating and cooking are relatively common exposures world-wide.
Conclusions
In conclusion, this study observed lowered AMH levels in association with smoking, adult ETS and burning wood and artificial firelogs in the home. These findings suggest that combustion by-products from common chronic exposures have toxic effects on the human ovary.
Supplementary Material
Acknowledgments
Sources of funding: This research was supported in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences (Z01-ES044005), the Avon Foundation (02-2012-085), the National Center for Advancing Translational Sciences (KL2-TR001109) and by the UNC Lineberger Cancer Control Education Program (R25 CA57726).
We would like to thank Dr. Janet Hall and Dr. Helen Chin for their helpful feedback on this manuscript.
Footnotes
Conflicts of Interest: None declared.
Formatted for Fertility and Sterility
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