Cumulative exposure to heavy metals and age at menopause

The onset of menopause is not only important by itself, but also because it is related to emotional, psychological, and health outcomes. The timing at which this transition takes place is particularly significant since premature (before age 40) or early menopause (before age 45) has been associated with an increased risk of cardiovascular heart disease, osteoporosis, mood, sexual health, and early mortality; while a later age at menopause has been associated with increased risk of endometrial cancer and all-cause mortality.

The influence of heavy metals on female reproductive ageing, including the timing of menopause, has been a subject of considerable research interest. Indeed, studies have observed the potential of these metals to induce premature ovarian insufficiency in women. However, research on the effect of the exposure to heavy metals on the age at which menopause occurs is scant and has yielded mixed results. Furthermore, a paucity of research has been observed on the impact of heavy metals on age at menopause, particularly among the Mexican population.

The main objective of this study is to assess the effect of the cumulative exposure to heavy metals on age at menopause. This study uses data from the 2018 Mexican Health and Aging Study (MHAS).  In 2018, a sub-group of the MHAS was selected to provide a hair sample for the purpose of examining exposure to heavy metals. The "MHAS 2018 Metal Exposures" dataset includes 2,671 samples from people aged 50 years and over, of whom 1,600 are women. The hair samples provide information on 14 metal levels (in μg/g). This study only considers those metals with less than 10% of missing values: chromium (6.4%), copper (1.0%), lead (1.8%), manganese (3.3%), nickel (4.3%), and titanium (1.0%). The relationship between metal concentrations and early and premature menopause was assessed using multivariate logistic regressions adjusted for known determinants of age at menopause (age, number of children, educational attainment, smoking status, alcohol drinking status, BMI, socioeconomic status, and exercise).

The results show that the mean age at menopause was 46.4 [95%IC (46.1, 46.7)] and that 21.8% and 11.4% of women experienced early menopause and premature menopause, respectively. No significant relationship was found between premature menopause and any of the heavy metals considered. However, there is some evidence that the odds of an early menopause are higher among women in the upper quartiles of hair lead and hair nickel concentrations, compared with those the lowest quartile. In adjusted analysis the odds of an early menopause were 1.8 [95%IC (1.1, 2.9)] and 2.0 [95%IC (1.3, 3.1)] for women in the third quartile of hair lead and hair nickel concentrations, respectively, compared with those in the first quartile. On the contrary, the odds of experiencing an early menopause among women in the upper quartile of hair chromium were 0.6 [95%IC (0.3, 0.8)] compared with those in the lowest quartile.