Scientists say that the rise in obesity could be partly to blame for the rise in infertility. Obesity can lead to many conditions, such as heart disease, diabetes, cancer and depression. If someone is overweight, the excess amount of fat cells and extra pressure put on the body interferes with hormone production. This can dramatically affect the fertility of a woman, as well as her ability to carry a baby to full term and the baby’s health post birth. But that’s not all; obesity can affect a man’s fertility too.
Obesity and fertility in Women
Women produce estrogen, the fertility hormone, via the ovaries and the adrenal gland. Put simply, ovarian estrogen production fluctuates according to the woman’s hormonal cycle, with periods of high fertility at certain times of the month, when estrogen levels cause eggs to be released. The adrenal gland makes a hormone called androstenedione, which is converted by fat cells into a kind of estrogen called estrone. If a person is very overweight or obese their extra fat cells convert more androstenedione into estrone. This confuses the reproductive system as the body constantly has high levels of estrogen—like hormones, interfering with the ovulation process and disrupting fertility.
Additionally, being overweight and excess estrogen can cause pre-cancerous changes in a woman’s womb, putting her at risk and further affecting fertility, although this complication, as with the excess estrone, is reversible with enough weight gain and medical treatment.
Obesity and fertility in Men
A 2008 study looking at the quality and quantity of men’s sperm discovered that 40% of men who had fertility problems were overweight, and a third obese. The study showed that obese men were three times more likely to have a low sperm count and that sperm they did have had motility problems or were misshapen. The combination of lower sperm count with less ability to swim and misshapen sperm could easily result in infertility in men.
One of the main causes of male infertility in obese people is the same as in females; the androstenedione. Just as with women, in men excess fat cells cause too much estrogen-mimicking estrone, which lowers testosterone levels and increases the female hormone estrogen. Higher estrogen levels in obese men cause men to develop breasts and, more importantly, reduce sperm production.
An additional factor in male obesity and fertility is that due to physiological and psychological issues, obese men tend to have a lower libido and may suffer from impotence.
Obesity in couples and sub-fertility
As many overweight or obese people tend to be married to an obese partner, it is important to assess the fertility risks on obese couples, not just obese men or women.
Sub-fertility (or subfecundity) is a term used to describe couples that take more than a year to conceive a baby whilst actively trying. A study in Denmark of nearly 50,000 couples showed that couples who were obese were nearly 3 times as likely to take more than a year to conceive, while overweight couples (with a BMI of 25-30) were 1.4 time more likely to take longer to conceive. Additionally, couples where the woman was obese but the man was underweight were nearly 4 times as likely to suffer from sub-fertility as couples of healthy weight.
The sub-fertility of obese couples could cause problems in populations as obesity levels rise and, with it, infertility in men and women.
Fertility and weight loss surgery
A 2010 study reported that weight loss surgery can increase the fertility of women who had difficulty conceiving prior to the operation, and that obese women who undergo weight loss surgery before conceiving are less likely to suffer from complications during pregnancy and after the birth.
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