Boxer shorts pack the best punch when you’re trying to conceive
If you are a man who is trying to have a child, you have probably already heard the advice about wearing loose fitting underwear. It may seem hard to believe that underwear can be so important, but last month the largest study on this topic so far confirmed that there is significant scientific evidence to support this recommendation. This study found that men who wear boxer shorts have higher sperm concentrations and sperm counts than other men [1. Minguez-Alarcon L, Gaskins AJ, Chiu YH, Messerlian C, Williams PL, Ford JB, Souter I, Hauser R, Chavarro JE. Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction. Internet. 2018. 33(9):1749-1756. Available from: https://academic.oup.com/humrep/article/33/9/1749/5066758].
The link between temperature and sperm cells
Temperature is important in sperm cell development. Have you ever wondered why testicles hang outside the body? It is because the testicles need to be at a lower temperature than the rest of your body in order to produce healthy sperm cells.
Scientists have previously found that higher temperatures have a negative effect on sperm cells [2. Hjolland NHI, Storgaard L, Ernst E, Bonde JP, Olsen J. Impact of diurnal scrotal temperature on semen quality. Reproductive Toxicology. Internet. 2002. 16(3):215-221. Available from: https://www.sciencedirect.com/science/article/pii/S0890623802000254]. Therefore the advice to wear looser fitting underwear when trying to conceive is based on trying to keep the temperature of the testicles lower. Tighter underwear results in higher temperatures for sperm cells and potential damage.
New research supports previous recommendations about underwear types
Dr Lidia Minguez-Alarcon and her team at Harvard T.H. Chan School of Public Health in Boston, USA, conducted the study on male partners of couples at a fertility centre in Boston. The study ran from 2000-2017 and it included 656 men aged 18-56 without a history of vasectomy.
The men provided a semen sample and blood sample. They also answered a questionnaire about the style of underwear they had worn most frequently over the previous three months.
Sperm concentration and sperm count results
53% of the men in the study wore boxer shorts. The rest of the men wore tighter fitting underwear, which included bikinis (very brief briefs), jockeys and briefs.
Men who wore boxer shorts had a statistically significant:
- 25% higher sperm concentration
- 17% higher total sperm count
- 33% more swimming sperm in a single ejaculate than the other men who wore tighter fitting underwear.
For these results, the team had already taken into account other factors which might have affected their findings. These factors included age, BMI, physical activity, hot baths, Jacuzzi use, the year the sample was taken and smoking status.
Additionally, the team found differences among the results of the ‘non-boxer shorts’ groups of men. The largest differences in sperm concentration were between men who wore boxer shorts and men who wore jockeys and briefs in particular.
Men who wore boxers also tended to have a higher percentage of motile sperm and a higher count of sperm cells which had a normal appearance, or morphology. However these results were not statistically significant.
FSH level results
The study also found that men who wore boxer shorts had lower levels of follicle-stimulating hormone (FSH) than the other men in the study. The serum FSH levels in men who wore boxer shorts were 14% lower than other men.
FSH is a hormone which is important in both male and female fertility. The pituitary gland in the brain produces FSH and releases it into the bloodstream. In men, FSH stimulates sperm production.
Therefore the team think that the higher FSH level in men who wore tighter underwear is part of a compensatory mechanism. This may be the body’s reaction to testicular damage from the high scrotal temperatures caused by wearing tight underwear.
When the team adjusted their results for FSH levels, the effect of tighter underwear on sperm quality was no longer present. Dr Minguez-Alarcon and her team believe that this supports the idea that damage to testicular function as a result of high temperatures may be responsible for FSH changes.
The team found that there was no relationship between the type of underwear and other markers of testicular function including serum reproductive hormones and sperm DNA integrity.
Why is this study important?
The results from this study are important because the team used data from a larger population size than previous studies. Dr Minguez-Alarcon and her team collected data from 656 men at a fertility clinic.
Another key feature of this study is that it did not just focus on semen quality. The team investigated a range of indicators of testicular function which previous studies have not included. Specifically, the team investigated reproductive hormones and DNA damage in sperm cells. This is valuable in developing a better understanding of the relationship between heat and sperm cell development.
Although these findings show a promising step forward in understanding factors which affect male fertility, there are some limitations. The men in this study were all from couples undergoing fertility treatment. Therefore the results may not be applicable to the general population of men. However it is important to note that men in the study generally had good semen quality, which the team measured using World Health Organisation guidelines .
Another issue is that there are other factors which could affect scrotal temperature which may be the reason behind these results. These possible factors include the material of underwear and the types of trousers worn (for example, skinny jeans).
Additionally, there are some flaws with the study itself. The team used a self-administered questionnaire for men to select the type of underwear they commonly wore, and this method of data collection leaves room for error. Furthermore, blood sampling was not limited to the morning. This means that the variation in levels of certain chemicals in the body at times of the day was not taken into account . This variation of chemical levels is called the circadian rhythm.
Dr Minguez-Alarcon and her team’s findings show an important step forward in understanding how lifestyle factors can affect male fertility. However scientists need to conduct more research to support these results and explore the relationship between underwear and FSH levels further.
For men who are trying to conceive, it would be ideal to wear boxer shorts to maximise the chances of having a baby. Improving your health can be difficult, but changing the type of underwear you choose is one of the easiest lifestyle modifications you can make.
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