Investigating the effect of diet on human sperm parameters and global sperm DNA methylation

Waddilove, Louise Elizabeth (2018) Investigating the effect of diet on human sperm parameters and global sperm DNA methylation. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Male fertility has been declining over the past 50 years, vindicating demand for further research into the aetiological agent(s) responsible for this reduction in sperm count and quality. It is suggested that modern lifestyle factors including diet & sedentary lifestyle are culpable. Veganism has gained recent popularity by those conscious of ethical food sourcing and the impact of the meat industry upon the climate. In addition to these environmental benefits, adoption of a vegan diet also confers health benefits. There have been associations between a plant-based diet and reduced risk of prediabetes and type 2 diabetes and reduced body mass index (BMI). Abnormal BMI is already well established to have negative effects on reproductive health. However, a lack of research into the effect of vegan diet on sperm methylation is yet to be explored. Male volunteers aged 22-40 years of age were recruited from the Manchester area, in reply to adverts placed around the university campus and through social media. Participants provided semen samples via masturbation and completed a food frequency questionnaire including questions regarding lifestyle, diet and biometrics. Participants were separated into cohorts according to self-reported dietary subscription. Omnivorous (n=5) and vegan (n=5). Sperm progressive motility, concentration, total sperm count, volume, pH and vitality were all measured. Sperm cells were isolated from semen via density gradient centrifugation; DNA was extracted from the sperm and an ELISA-based assay to assess sperm global methylation status was performed. Means of sperm parameters were compared via unpaired t-tests for the two dietary cohorts, as were means of the global methylation data for the two dietary cohorts. Biometrics & Lifestyle factors were evaluated as potential confounding factors via unpaired t-tests and Fisher’s contingency test. None were significant and therefore did not need to be controlled for. All data collected were also pooled into a combined cohort, and correlational analyses and linear regression performed to identify any associations between sperm parameters and global methylation, biostatistics & lifestyle factors and global methylation, sperm parameters and biostatistics & lifestyle factors, and interactions between sperm parameters all within the combined cohort. Statistically significant positive correlations were observed between combined cohort sperm progressive motility and concentration (r=0.7766, p=0.0082**) and sperm motility and vitality (r=0.6535, p=0.0404*). No other statistically significant correlations were identified in the analysis of this study. The key aim of this pilot study was to determine whether subscription to an omnivorous or vegan diet has any significant effect on the methylation signature and quality of human sperm DNA. No such relationship was demonstrated in the results of this study, with no significant differences in sperm parameters or sperm DNA global methylation between omnivorous and vegan diets. This research alone suggests that subscription to an omnivorous or vegan diet has no bearing on the quality or methylation level of sperm DNA. Moving forward, further research should be carried out within a larger population to confirm these findings.