Sperm are influenced by diet, and
the effects arise rapidly. This is the conclusion of a study by researchers at
Linköping University, in which healthy young men were fed a diet rich in sugar.
The study, which has been published in PLOS Biology, gives new insight
into the function of sperm, and may in the long term contribute to new
diagnostic methods to measure sperm quality.
“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 to two weeks”, says Anita Öst, senior lecturer in the
Department of Clinical and Experimental Medicine at Linköping University, and
head of the study.
Sperm quality
can be harmed by several environmental and lifestyle factors, of which obesity
and related diseases, such as type 2 diabetes, are well-known risk factors for
poor sperm quality. The research group that carried out the new study is
interested in epigenetic phenomena, which involve physical properties or levels
of gene expression changing, even when the genetic material, the DNA sequence,
is not changed. In certain cases such epigenetic changes can lead to properties
being transferred from a parent to offspring via the sperm or the egg.
In a previous
study, the scientists showed that male fruit flies which had consumed excess
sugar shortly before mating more often produced offspring who became
overweight. Similar studies on mice have suggested that small fragments of RNA
known as tsRNA play a role in these epigenetic phenomena that appear in the
next generation. These RNA fragments are present in unusually large amounts in
the sperm of many species, including humans, fruit flies and mice. So far, their
function has not been examined in detail. Scientists have speculated that the
RNA fragments in sperm may be involved in epigenetic phenomena, but it is too
early to say whether this is the case in humans. The new study was initiated by
the researchers to investigate whether a high consumption of sugar affects the
RNA fragments in human sperm.
The study
examined 15 normal, non-smoking young men, who followed a diet in which they
were given all food from the scientists for two weeks. The diet was based on
the Nordic Nutrition Recommendations for healthy eating with one exception:
during the second week the researchers added sugar, corresponding to around 3.5
litres of fizzy drinks, or 450 grammes of confectionery, every day. The sperm
quality and other indicators of the participants’ health were investigated at
the start of the study, after the first week (during which they ate a healthy
diet), and after the second week (when the participants had additionally
consumed large amounts of sugar).
At the beginning
of the study, one third of the participants had low sperm motility. Motility is
one of several factors that influence sperm quality, and the fraction of people
with low sperm motility in the study corresponded to that in the general
population. The researchers were surprised to discover that the sperm motility
of all participants became normal during the study.
“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 healthly diet that has a positive effect on the sperm”, says Anita
Öst.
The researchers
also found that the small RNA fragments, which are linked to sperm motility,
also changed. They are now planning to continue the work and investigate
whether there is a link between male fertility and the RNA fragments in sperm.
They will also determine whether the RNA code can be used for new diagnostic methods
to measure sperm quality during in vitro fertilisation.
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