Friday June 12 2009
“Men who gorge on steak, burgers and full-fat cream have such poor quality sperm they stand little chance of fathering a child,” according to The Daily Telegraph. The news is based on a study of 61 men, which found that a diet containing antioxidant-rich vegetables improved the quality of their sperm.
The study found that men with normal sperm had higher intakes of carbohydrates, fibre, folate, vitamin C and lycopene than men with low sperm counts and abnormal sperm. Those with normal sperm also had a lower intake of proteins and of total fat. The study does not make a direct link between red meat and sperm quality, as the newspapers imply.
Researchers looked at men’s estimates of their food intake and calculated the amount of certain nutrients they were consuming. Although they found that men with abnormal sperm had higher protein intake, this protein could have come from several sources of food.
The study was small and has limitations because of its design. This research should be regarded as preliminary evidence, and larger studies will be needed to explore whether diet does affect semen quality.
Where did the story come from?
This research was conducted by Dr Jaime Mendioloa and colleagues from Instituto Bernabeu and other medical and academic institutions in Spain. The study was supported in part by a number of Spanish institutions, including the Seneca Foundation and the Department of Education and Culture of Murcia. It was published in the peer-reviewed medical journal Fertility and Sterility.
What kind of scientific study was this?
This was a case-control study investigating the effects of diet on semen quality.
In the study, 30 men with poor-quality semen (the case group) were compared with a control group of 31 men with healthy sperm. Men were recruited through fertility clinics in Murcia and Alicante in Spain. The men in the case group had a mix of severe and moderate oligozoospermia (a low sperm count of less than 20 million sperm/ml) and severely abnormal sperm (less than 6% normal sperm). Men in the control group had normal sperm (20 million or more sperm/ml and more than 13% normal forms).
The men provided two semen samples, with an interval of between seven days and three weeks between the two collections. Various analyses were performed on the sperm samples, including ejaculate volume, sperm concentration and percentage of motile (capable of moving) sperm. The sperm were also examined using a microscope. The participants underwent a physical examination where height and weight were measured and information was collected on occupational history.
A food frequency questionnaire was used to assess how frequently the men had consumed various foods in the previous year, with responses ranging from “never or less than once a month” to “six or more times per day”. Responses were converted into estimates of nutrient intake (for protein, carbohydrates, vitamins, minerals etc) by multiplying the quantity of the food consumed by its nutrient composition, which was derived from food composition tables. Alcohol intake was also assessed through the food frequency questionnaire.
The researchers then used statistical methods to assess the link between semen quality and nutrient intake while adjusting for a number of other factors that may have affected the relationship (confounders). These included smoking, age, previous occupational exposure and total energy intake.
What were the results of the study?
The authors found that the men with normal sperm had higher intakes of carbohydrates, fibre, folate, vitamin C and lycopene. They also had lower intake of proteins and of total fat.
What interpretations did the researchers draw from these results?
The researchers concluded that a low intake of antioxidant nutrients, found in fruit and vegetables, was associated with poor semen quality in Spanish men attending fertility clinics.
What does the NHS Knowledge Service make of this study?
This small case-control study investigated a link between the intake of certain nutrients and the quality of sperm. There are several important points to bear in mind when interpreting the results of this research:
- This type of case-control study cannot prove causation (in other words, that the men’s diets were responsible for the quality of their sperm). While the researchers adjusted for some of the obvious confounding factors, unmeasured factors may have influenced the result.
- Case-control studies are prone to recall bias, meaning that participants may not have accurately remembered their past food intake. In this study, the men were asked how much they ate of certain food groups over the past year. Their recall of this is unlikely to have been 100% correct. Other information, like occupational exposures, may not have been accurately recalled either.
- This was a small study and, as such, estimates of the association between semen quality and nutrient intake are not very precise. The researchers are very cautious in their conclusions from this study. They say that the results suggest that “poor semen quality may be associated with a lower intake of carbohydrates, fibre, folate, vitamin C, and lycopene and a higher intake of protein and total fat”, and that overall “a low intake of antioxidant nutrients might seem to have a negative effect on semen quality.”
While this study may provide some preliminary evidence of a link between certain nutrients and the quality of sperm, it has limitations and the findings need to be confirmed in larger prospective studies.