Being Underweight May Impact Male Fertility

A new study, published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology, shows that being underweight may have a detrimental impact on male fertility.

Several prior studies have shown that being overweight can impact male fertility, but this study shows that being underweight might be worse.  Men with a body mass index (BMI) at or below 18.5 kg/m2 were found to have sperm counts which were 7 percent lower than men with normal BMIs.  Men who were overweight had sperm counts that were 4 percent lower than men with normal BMIs.

The study looked at 3,966 male sperm donors at a sperm bank in China, who were all weighed at the time of sperm donation.  The men were split into four groups: Underweight with a BMI of 18.5 kg/m2, normal weight with a BMI of 18.5 – 24.9 kg/m2, overweight with a BMI of 25 – 29.9 kg/m2, and obese with a BMI of 30 kg/m2 and above.

Compared to men with a normal BMI, men in the underweight group showed a 3 percent lower sperm concentration, 7 percent lower total sperm count, and 7 percent lower total motile sperm count.  Men who were overweight faired a little better in 2 categories.  They had a 3.9 percent lower total sperm count and 3.6 percent lower total motile sperm count compared to men with normal BMIs.  Sperm concentration for overweight men was worse than for underweight men though.  Compared to men with normal BMIs, men who were overweight had sperm concentrations that were 4.2 percent lower.

“Our study provides evidence that being underweight and overweight are both associated with lower semen quality, and highlights the importance of maintaining normal weight for men,” said lead author Dr. Yuewei Liu of the Huazhong University of Science and Technology.

This study is an important reminder to stay healthy, but not overdo weight loss and exercise. For more information on how diet and lifestyle can impact fertility, visit our Lifestyle and Fertility page.

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