Obesity continues to be a rising problem in the US. It can result in a number of negative health effects that can shorten life expectancy like diabetes, hypertension, and can even alter the functionality of sperm in men. With fertility levels in recent decline for both women and men it’s important to understand all factors that contribute to healthy reproduction.
While correlation does not necessarily mean causation, the relationship between fertility and obesity is important to focus on, and it is of interest to identify how lifestyle factors can be contributing to this fertility decline—and on what timescale these effects occur. It can also be interesting to note what lifestyle factors can help alleviate any problems.
In men, sperm production, morphology, movement, and function are key aspects of fertility that can be affected, since sperm are the primary effectors of fertilization. Researchers at Linköping University chose to examine sperm motility, focusing on the epigenetic effects that a man’s diet can have on sperm health. Their findings were enlightening.
As Anita Öst, study lead and senior lecturer in the Department of Clinical and Experimental Medicine, notes, “We see that diet influences the motility of the sperm, and we can link the changes to specific molecules in them. Our study has revealed rapid effects that are noticeable after one or two weeks.”
How was the experiment carried out?
The researchers looked at 15 healthy, non-smoker males who strictly adhered to a diet comprised of food administered by the research team. After their health was established at the beginning of the study—including the motility of their sperm—they were given a diet that followed the Nordic Nutrition Recommendations. In the second week, they followed the same diet but with one change: the addition of 450g of sugar every day. The health indicators were re-examined after the first and second weeks.
The principal finding was that, while one-third of participants had low sperm motility at the start of the study, by the end all participants had normal sperm motility.
Ost continued, “The study shows that sperm motility can be changed in a short period, and seems to be closely coupled to diet. This has important clinical implications. But we can’t say whether it was the sugar that caused the effect, since it may be a component of the basic healthy diet that has a positive effect on the sperm.”
What were the epigenetic changes noted?
The team noted that the DNA sequence was not changed in the short 1 week window, so they turned to the epigenetic relationship between RNA and cell function to understand the differences in gene expression responsible for poor sperm quality.
RNA plays a critical role in silencing chromatin germ cells, which can affect gene expression. RNA is a critical gauge of cellular function—and indicators of how changes are being carried out.
They found that a type of small noncoding RNA called tRNA-derived small RNA (tsRNA), in the sperm were upregulated after the high-sugar diet, which directly affected several pathways, including one associated with mitochondria, therefore highly significant in any examination of metabolic health on a cellular level. The association with mitochondria was further strengthened by the upregulation of rRNA-derived smallRNA (rsRNA) in mitochondra.
Interestingly enough, this tsRNA upregulation was found to be associated with increases in sperm motility, but negatively correlated with obesity. This is very important context within the greater discussion of the obesity epidemic.
Further characterization is needed to understand how RNA fragments can affect male fertility. Additionally, it will be interesting to see if these RNA fragments can be used to develop a diagnostic test to gauge sperm quality for anyone pursuing in vitro fertilization methods.
Source: Nätt D et al. (2019) Human sperm displays rapid responses to diet. PLoS Biol 17(12)
Reference: Karin Söderlund Leifler “Diet has rapid effects on sperm quality ”. Linköping University News. 02 Jan 2020. Web.
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