The adverse effects of obesity on reproduction

Abstract

Obesity (defined as a body mass index (BMI) of R30 kg/m) is perhaps the major health challenge facing resource-rich countries. Obesity is a major cause of ill health and mortality in countries where it is prevalent, largely via increased rates of ischaemic heart disease, stroke, diabetes, hypertension and osteoarthritis, with cancer (particularly colon and breast) also playing a role (Haslam & James 2005). The current prevalence of obesity in the UK is around 20%, somewhat behind that of the USA at 34% (Flegal et al. 2010), but rates are rapidly increasing in both countries. The Foresight report, commissioned by the UK government, indicated that in the absence of substantial intervention, rates of obesity would continue to increase in the UK to around 50% in the adult population by 2050, with the annual NHS costs of obesity projected to be £10 billion by 2050, and societal costs to be £49 billion by 2050 (Government Office for Science 2007). In contrast to its effects on other areas of health, the impact of obesity on reproduction has received less attention. In this focus issue, we review both the influence of obesity on reproductive performance and the current knowledge of mechanisms by which obesity exerts its adverse effects. Understanding these issues should allow targeted therapies to be developed to improve reproductive health between the obese and their offspring. Perhaps the most well-established connection between obesity and reproductive problems is the link between obesity and infertility, as reviewed by Brewer & Balen (2010). Obesity decreases successful pregnancy rates in both natural and assisted conception cycles, with fertility being partially restored if weight loss can be achieved. The mechanism(s) by which obesity reduces pregnancy rates are complex and likely multifactorial. Insulin resistance appears to be a key factor to obesityinduced anovulation, with high levels of insulin leading to low levels of sex hormone-binding globulin, hyperandrogenaemia and high levels of free insulin-like growth factor 1. The loss of as little as 5% of body weight is accompanied by an increase in ovulation rates and reduces biochemical abnormalities. Elevated levels of leptin and low levels of adiponectin have also been implicated in the mechanism by which obesity reduces