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Underweight women are at greater risk of early menopause
Underweight women and women who were underweight as teenagers or in their mid-30s are at greater risk of experiencing an early menopause compared to lean or normal weight women, according to a study of nearly 80,000 women.
In addition, underweight women who lost 20 pounds or more at least three times between the ages of 18 and 30 were at significantly increased risk of an early menopause, which is defined as a naturally occurring menopause before the age of 45.
The study, which is published today (Thursday) in Human Reproduction [1], one of the world’s leading reproductive medicine journals, is one of very few studies to follow women prospectively from as young as 25 to menopause, and is the largest ever to do so. Information from their teenage years was also gathered.
“Our findings suggest that women who are underweight in early or mid-adulthood may be at increased risk for early menopause. Up to 10% of women experience early menopause and it is associated with a higher risk of cardiovascular disease, and other health conditions such as cognitive decline, osteoporosis and premature death, so these findings have important implications for women and their doctors,” said Dr Kathleen Szegda, who, at the time the study was completed, was a post-doctoral research associate at the University of Massachusetts, USA, and led the research. “Underweight women may want to consider discussing the potential implications of these findings with their doctors.” [2]
The researchers looked at body mass index (BMI), weight distribution, weight change and timing of menopause in 78,759 premenopausal women aged between 25-42 who joined the US Nurses’ Health Study II in 1989. The women provided information on their medical history and health-related behaviours such as smoking and exercise at the time of joining the study, and then they updated the information by means of questionnaires every two years thereafter. The researchers followed them until 2011, by which time 2804 women had reported early natural menopause.
They found that women who were underweight at any age (BMI of less than 18.5 kg/m2) had a significant 30% increased risk of early menopause compared with lean or normal weight women (BMI between 18.5-22.4 kg/m2). Overweight women with BMIs between 25-29.9 kg/m2 had a 21-30% lower risk of early menopause compared to normal weight women.
Women who were underweight at 18 with a BMI of less than 17.5 kg/m2 had a 50% higher risk of early menopause compared to lean or normal weight women; women who had a BMI of less than 18.5 kg/m2 at the age of 35 had a 59% increased risk.
Underweight women who reported losing 20 pounds or more, three times or more between the ages of 18 and 30, had a 2.4-fold increased risk of early menopause; however, there were only seven women who reported this and so, although the result is statistically significant, it still needs to be treated with caution.
Dr Szegda concluded: “Causes of early menopause are not clearly understood. Our findings suggest that being underweight may have an impact on the timing of menopause. More research is needed to understand how it increases the risk of early menopause.”
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Gita Mishra is Professor of Life Course Epidemiology, Director of the Australian Longitudinal Study on Women’s Health and Deputy Head of the School of Public Health at The University of Queensland
The results need to be interpreted with caution as the observed association between underweight women and early menopause could be due to a common cause or shared risk factors, such as an adverse childhood environment. So in this case 'underweight' might be a marker of the poor environment.
The press release mentions 'risk', but these results can only be interpreted as odds ratio, which is a measure of association between BMI and age at menopause. If the results were presented as relative risk, then we would expect the figure to be less than 30% (as relative risk is usually smaller than the corresponding odds ratio))
Data from the Australian Longitudinal Study on Women’s Health has shown that among women born from 1989-95 (currently aged 22-27 years), 20 per cent were obese while less than 5 per cent were underweight. Therefore, at a population level obesity will pose a greater health burden than the underweight.
Professor Michael Chapman is Professor of Obstetrics and Gynaecology at the School of Women's & Children's Health, University of New South Wales, and at St George Public Hospital
Around five per cent of women reach natural menopause before the age of 45 years. Most biological events in life – such as menarche or birth weight – follow a bell shaped curve. Generally early menopause is assumed to be at the bottom end of the bell shaped curve.
This statistical analysis uses a large, long term cohort study of nurses to assess the impact of weight on age at menopause. Using sophisticated statistics looking at multiple variables, the researchers conclude that low BMI at 18 years and at 35 years increases the risk of menopause before 45 by 30%. The researchers offer little in explanation, other than that small babies tend to remain small later in life, and may have been endowed with fewer eggs in utero.
However, translating their statistics into numbers of actual women who might be affected, low BMI might affect 2 extra women undergoing early menopause per 1000 women in the general population. Thus, the clinical significance of this study is low.
