Obesity and reproductionBMJ 2006; 333 doi: https://doi.org/10.1136/bmj.39049.439444.DE1 (Published 30 November 2006) Cite this as: BMJ 2006;333:1159
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To the editor:
Obesity and male reproduction
The review by Ramsay et al  on obesity and reproduction describes a negative effect of obesity on erectile function but does not discuss the effect of obesity on sperm quality and fertility.
The effects of obesity on male reproduction are less well documented than in the female. However, several studies indicate that sperm quality and fertility are reduced in overweight and obese men (Body mass index “BMI” 25-30 kg/m2 and >30 kg/m2 respectively).
A BMI >25 in oligzoospermic men (sperm concentration less than 20 million/ml) has been associated with decreased sperm concentration and reduced testosterone/estradiol ratio, suggesting that excessive conversion of testosterone into estradiol by the enzyme aromatase in peripheral bodily fat may be a cause of impaired sperm quality . Disturbed testicular thermoregulation has also been proposed as a mechanism for impaired testicular function in obese men [review: 3].
Data from healthy men indicate higher levels of sperm DNA damage in overweight and obese men, coupled with lower numbers of normal motile spermatozoa per ejaculate 
Recent data from the Agricultural Health Study in the United States indicate, after adjusting for potential confounders, that a 3-unit increase in male BMI was significantly associated with infertility (odds ratio 1.12). There was a dose–response relationship and the association between BMI and infertility was similar for older and younger men, suggesting that erectile dysfunction in older men does not explain the association .
In fact, both extremes of BMI (< 19 or > 30 kg/m2) have been associated with reduced testicular volume  and reduced semen quality (BMI < 20 or > 25 kg/m2), suggesting impairment of spermatogenesis .
In addition to their possible role as a cause of male infertility and anomalies of the male genital tract, the chemical calorie theory suggests that endocrine disruptors are, at least in part, responsible for the pandemic of obesity in the last few decades .
 Ramsay JE, Greer I, Sattar N. ABC of obesity. Obesity and reproduction. Br Med J 2006; 333: 1159-62.
 Fejes I, Koloszar S, Zavaczki Z, Daru J, Szollosi J, Pal A. Effect of body weight on testosterone/estradiol ratio in oligozoospermic patients. Arch Androl 2006; 52: 97-102.
 Baker HW. Reproductive effects of nontesticular illness. Endocrinol Metab Clin North Am 1998; 27: 831-50.
 Kort HI, Massey JB, Elsner CW et al. Impact of body mass index values on sperm quantity and quality. J Androl 2006; 27: 450-2.
 Sallmen M, Sandler DP, Hoppin JA, Blair A, Baird DD. Reduced fertility among overweight and obese men. Epidemiology 2006; 17: 520-3.
 WHO. Towards more objectivity in diagnosis and management of male infertility. Int J Androl 1987; suppl. 7.
 Jensen TK, Andersson AM, Jorgensen N et al. Body mass index in relation to semen quality and reproductive hormones among 1,558 Danish men. Fertil Steril 2004; 82: 863-70.
 Baillie-Hamilton PF. Chemical toxins: a hypothesis to explain the global obesity epidemic. J Altern Complement Med 2002; 8: 185-92.
Competing interests: None declared
Competing interests: No competing interests