Reviewed research

Authors Paasch W, Grunewald S, Kratzsch J, Glander H-J

Review Date Feb 2011

Citation Fertility and Sterility 2010:94(7):2898-2901 (December 2010)



Age-related testicular alterations have been shown to be associated with poorer semen parameters and decreased testosterone levels. The association between body mass index (BMI) and sperm quality or number is not clearly defined. 



The aim of this study was to examine the relationship between BMI, age, semen quality, and fertility-related hormones in a large group of patients undergoing investigations for infertility.



A case-cohort study of 2,157 patients being investigated for infertility, aged 17-67 years, was performed to assess the impact of BMI and age on male fertility.

The following semen parameters were measured: total sperm counts (TSC); total count of sperm with normal morphology (TCN); percent of motile spermatozoa. Serum concentrations of testosterone (T), inhibin-B, LH and FSH were also measured.

Unpaired Mann-Whitney U-tests were used to test differences in various sperm and hormone measures across BMI groups. Spearman rank correlation coefficients were calculated to look at associations between pairs of linear variables. Multiple linear regression was performed with BMI and age as dependent variables and an age x BMI interaction term.



Based on BMI categories, 5% of the cohort was underweight, 46% normal weight, 38% overweight and 11% obese. Age increased across BMI groups. TSC and TCN were lower in overweight and obese men compared to normal weight.Obese men also had significantly lower serum concentrations of T and inhibin-B.

Multiple regression analysis across the total cohort showed only age to be significantly correlated with all spermiogram parameters and serum hormones, but in patients aged 20-30 years (n = 617) the total sperm count was significantly negatively correlated with body mass index.



The study showed that semen quality in general was more closely associated with age than BMI. However, a normal BMI appeared to be related to total sperm count in men of prime reproductive age i.e. 20-30 years.


Points to Note
  1. The association between age and BMI can confound associations between BMI and sperm and hormone parameters unless adequate adjustment is made in analysis or appropriate cohorts are studied.
  2. The multiple regression models used in this study were not made very explicit so it is difficult to assess what multivariable adjustments were made. The conclusions therefore need to be treated with caution.
  3. No men of normal fertility were included in the study.
  4. There was a relatively small proportion of obese men in the cohort which may have precluded seeing stronger associations with obesity.
  5. The main outcome of the study was to highlight that age is important to consider when assessing BMI/fertility associations.


Website: http://www.ncbi.nlm.nih.gov/pubmed/20667533

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