Thursday October 31 2013
Beta-carotene gives carrots their bright orange colour
"The secret to healthy sperm? Carrots," the Mail Online website declares. The study it reports on found that certain vegetables may help improve sperm quality.
The researchers carrying out the study were interested in two important aspects of sperm quality:
- sperm motility – how quickly a sperm can swim towards an egg
- sperm morphology – the size and shape of a sperm (for the best chance of successfully conceiving, a sperm should have an oval head and a long tail)
They looked at young men’s diets and analysed their sperm samples. They found that men who ate a higher amount of three antioxidants found in fruit and vegetables had sperm with better motility and morphology.
The three antioxidants in question were:
- beta-carotene – found in carrots, lettuce and spinach
- lutein – found in lettuce and spinach
- lycopene – found in tomatoes
Men who ate higher levels of beta-carotene and lutein had a 6.5% increase in sperm motility, and those who consumed higher levels of lycopene had 1.7% improved sperm morphology.
However, this study examined diet and sperm quality at the same time, so cannot prove cause and effect. Also, the study involved young healthy men so the results may not apply to different populations. Still, increasing your intake of vegetables is unlikely to harm you or your sperm, and has many other health benefits.
Where did the story come from?
The study was carried out by researchers from Harvard School of Public Health and Universities in Canada, Copenhagen, Murcia and New York. It was funded by a grant from the National Institutes of Health and the European Union. The study was published in the peer-reviewed medical journal Fertility and Sterility.
The Mail Online’s claim that carrots boost sperm performance “more than any other fruit or veg” is not supported by the results of the study. The researchers only looked at the influence of a small range of antioxidants and vitamins. It could be the case that other dietary antioxidants are more effective.
The Mail Online also doesn’t explain that the cross-sectional study design cannot prove that eating carrots has a direct effect on sperm. It also glosses over the fact that other types of fruit and veg, such as tomatoes, lettuce and spinach, may also be beneficial.
What kind of research was this?
This was a cross-sectional study looking for a potential association between a diet high in antioxidants and the quality of sperm.
As this was a cross-sectional study it cannot prove causation.
It cannot prove that the antioxidants caused better quality semen, as the relationship between the two is likely to be influenced by a variety of other confounding health and lifestyle factors.
Ideally, a randomised controlled trial would be carried out to prove cause and effect. However, such a trial randomising men to different diets and then following them up over months or years to examine their sperm quality may not be feasible or ethical.
What did the research involve?
The researchers recruited 389 young men from university and college campuses in Rochester, New York. A 131-item food frequency questionnaire at the start of the study was completed by only 194 of the men. Men were further excluded if they did not provide information on calorie intake, or if their calorie intake was less than 600 kcal or more than 15,000 kcal a day. The total sample size was 189 men with an average age of 19. Men were paid $75 to participate.
Each man provided a semen sample which was analysed within half an hour for:
- semen volume
- sperm count
- sperm motility
- sperm morphology
From the food and supplement frequency questionnaire, the researchers estimated the amount of the following micronutrients in their diet:
- vitamin A
- vitamin C
- vitamin E
- carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein and lycopene)
The researchers then performed statistical analyses to look for links between the amount of each micronutrient consumed and semen quality.
They took into account confounders such as age, body mass index (BMI), physical activity level, caffeine intake, alcohol intake and current smoking status. They also analysed the effect of how long the men had abstained from sexual activity (including masturbation) before the semen sample was provided.
What were the basic results?
Increased carotenoid intake, especially beta-carotene and lutein, was associated with sperm that moved 6.5% faster (95% confidence interval (CI) 0.6–12.3) compared with those from men with the lowest carotenoid intake. This association was higher if the intake came from food rather than supplements.
Lycopene intake was associated with 1.7% (95% CI -0.1 to 3.6) higher numbers of normally-shaped sperm compared with men with the lowest intake.
High intake of vitamin C (from food only) was associated with lower sperm count. The sperm concentrations were 22% (95% CI -47-16) lower than in the men with the least intake of vitamin C.
However eating a bit more vitamin C produced the highest sperm concentration, count and motility. Vitamin C was not related to any change in sperm shape.
No associations were seen with intake of vitamin A or E, and none of the results were affected by BMI or smoking status.
Three foods (carrots, lettuce and spinach) accounted for 59% of the beta-carotene intake and two foods (lettuce and spinach) accounted for 56% of the lutein. The majority (98%) of the lycopene was in five foods (tomato soup, tomato juice, salsa, ketchup and fresh tomatoes).
How did the researchers interpret the results?
The researchers describe a relationship between higher intakes of the carotenoids beta-carotene and lutein and greater sperm motility, and between higher intake of lycopene and increased number of normal-shaped sperm. They point out that this research does not prove that increased intake improves motility or shape of sperm and they do not know what effect, if any, increased consumption of these nutrients would have on men with fertility problems.
This study shows an association between higher dietary consumption of food that contains more carotenoids and slightly better sperm motility and greater number of sperm with normal shape.
However, these associations were small. For example, the World Health Organization defines sperm samples as adequate if the average number of sperm with a normal shape is 4% or more. In this group of young men, the average was 9% (5–12%), and was only 1.7% higher in men eating more food containing lycopene.
There are other important limitations, including the following.
- As all assessments of dietary intake were self-reported, it is possible that estimations of carotenoid intake may have been inaccurate.
- The study has a cross-sectional design, which means it cannot prove cause and effect. As the researchers acknowledge, the observed relationship between sperm quality and dietary factors is likely to be influenced by confounding from other factors such as another substance in the food that is improving sperm quality, or other healthy lifestyle behaviours.
- The study was conducted in a sample of only 189 young men from one US region, who had an average age of 19 and none of whom had reported fertility problems. It is not known whether similar associations between carotenoid intake and sperm quality would be obtained from other samples of men, for example those of different ages, or those with fertility problems.
- In this sample of young men it is not known whether the observed differences in sperm quality would have led to any difference in the likelihood of successful pregnancy if they were trying to conceive with a partner.
While the media has focused on the carrots, the study reports that 59% of the dietary intake of beta-carotene came from carrots, lettuce and spinach. The lettuce and spinach were also the sources of 56% of the lutein. While this study does not prove that any of these vegetables had a direct effect on sperm quality, increasing your intake of vegetables is unlikely to cause any harm.
Analysis of the relationship between vitamin C and sperm quality gave a very wide range of results. Previous studies have shown that vitamin C can improve the motility and number of sperm of normal shape. Other studies have shown that it has no effect. Until results are more conclusive, it is best to eat the daily recommended amount of fruit and vegetables.
The researchers conclude that a well-designed randomised controlled trial is required to determine whether eating more carotenoids improves sperm morphology and motility.
However, eating a diet rich in fruit and vegetables is certainly not going to cause you any harm.
Other ways to improve your sperm quality include:
- quit smoking if you smoke
- try to achieve or maintain a healthy weight
- drink sensibly
- keep your testicles cool
Read more advice about improving your sperm quality.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.