Tuesday August 27 2013
Raspberries are rich in micronutrients, including vitamin C
"Eating raspberries could increase your chances of becoming a father," the Mail Online website reports, with the Daily Express making similar claims. But these claims are not backed up by the evidence, as the stories seem to be based on the opinion of just one fertility nutritionist.
The story comes from a small study published in 2012 that looked at whether the self-reported micronutrient intake (daily intake of vitamin C, vitamin E, beta-carotene, zinc and folate) of 80 men was associated with sperm DNA damage – in other words, sperm quality. Poor sperm quality can lead to male infertility.
Although this study found that men with a high dietary and supplement intake of certain micronutrients had sperm with less DNA damage, it was unable to show a cause and effect relationship.
This study didn't specifically investigate raspberries – the fruit wasn't even mentioned once in the study. Crucially, none of the 80 men involved in the research actually had fertility problems, regardless of any differences seen in their results.
A healthy balanced diet containing fresh fruit and vegetables has many health benefits, but there is no basis for reports that raspberries boost fertility. The way this study has been covered illustrates the systematic problems with medical reporting in the media. Read more about how medical reporting is subject to spin.
Where did the story come from?
The study was carried out by researchers from the Lawrence Berkeley National Laboratory, the Lawrence Livermore National Laboratory and the University of California in the US, and the University of Bradford in the UK. It was funded by the US National Institute of Environmental Health Sciences. The study was published in the peer-reviewed journal, Fertility and Sterility.
This story was reported by the Daily Express and the Mail Online website and seems to be based on the opinion of one fertility nutritionist.
The Mail Online goes on to include a quote from British Summer Fruits on how "tasty and juicy" raspberries have been this year – a matter of opinion rather than scientific fact.
The Daily Express also carried a story about raspberries boosting fertility, but in this case it was solely based on the opinion of the fertility nutritionist.
What kind of research was this?
This was a cross-sectional study that aimed to investigate whether lifestyle factors, such as dietary intake of micronutrients, are associated with sperm DNA damage.
Cross-sectional studies can tell us whether men with sperm with the most or least DNA damage have different micronutrient intakes, but cannot show us how or whether these two things are directly linked.
As cross-sectional studies only look at a snapshot in time, we don't know if the men have always had the diet they reported, or whether it is diet or another factor that is responsible for the differences seen in sperm quality.
A randomised control trial (RCT) would be required to provide better evidence about whether micronutrient intake influences sperm quality.
What did the research involve?
The researchers studied a group of 80 non-smoking men, aged between 20 and 80 years old, who reported no fertility problems. All the men were or had been employees of a national laboratory in California.
The men completed a questionnaire on sociodemographic characteristics (age, ethnicity and education), occupational exposures, medical and reproductive histories, and lifestyle habits.
They also completed a food frequency questionnaire so that their daily dietary and supplement intake of micronutrients (vitamin C, vitamin E, beta-carotene, zinc and folate) could be calculated.
The men also provided a sperm sample. Any damage to sperm DNA was measured using two different techniques: alkaline and neutral DNA electrophoresis. Both techniques can be used to assess DNA quality.
Alkaline DNA electrophoresis is thought to detect DNA damaged by double strand breaks (where both DNA strands are cut), single strand breaks, or other forms of DNA damage. Neutral DNA electrophoresis is thought to mainly detect double strand breaks.
Micronutrient intake was classified as low (below 25%), moderate (25% to 75%) or high (above 75%), and the researchers investigated whether men with different intakes had sperm with different amounts of DNA damage. Analyses were adjusted for sociodemographic characteristics, occupational exposures, medical and reproductive histories, and lifestyle habits.
What were the basic results?
The researchers found no significant association between any measure of micronutrient intake and sperm DNA damage measured using neutral DNA electrophoresis.
When DNA damage was measured using alkaline DNA electrophoresis, it was found that men with a high intake of vitamin C had 16% less sperm DNA damage than men with a low intake.
Men with a high intake of vitamin E, folate or zinc also had less sperm DNA damage than men with a low intake, but the difference was not statistically significant.
When antioxidants (vitamin C, vitamin E and beta-carotene) were considered together, men with a high intake had significantly less sperm DNA damage than men with a low intake.
The researchers then looked at men aged more than or less than 44 years of age. Older men had more sperm DNA damage. Older men (over 44 years) with an above average vitamin C or zinc intake had less sperm damage compared with older men with a less than average intake.
Vitamin E intake showed a similar pattern, but the differences were not significant. The older men with an above average intake of these micronutrients showed levels of sperm DNA damage that were similar to those of the younger men. However, younger men (under 44 years) did not benefit from an above average intake of the micronutrients surveyed.
How did the researchers interpret the results?
The researchers concluded that, "Men with higher dietary and supplement intake of certain micronutrients may produce sperm with less DNA damage, especially among older men."
They go on to say that, "These new findings suggest that for men who are at increased risk of DNA strand damage due to advancing age, a diet that consists of high levels of antioxidants and micronutrients may decrease the risk of producing sperm with DNA damage."
This cross-sectional research suggests that men with higher intakes of certain micronutrients have sperm with less DNA damage – in other words, their sperm is of a better quality.
But there are limitations to this research. The main drawback is that the research was a small cross-sectional study of 80 men. Cross-sectional studies cannot show cause and effect relationships – a randomised controlled trial would be required for this.
As the researchers also point out, because of the correlation between the intake of different nutrients, it is difficult to determine whether the results seen are because of an overall high-quality diet, from one nutrient or certain nutrients in particular, or from one or several associated lifestyle factors.
It is also important to note that regardless of any differences seen in sperm DNA, none of the 80 men studied actually had reported fertility problems.
However, this research does not really provide the evidence to back up the news that raspberries boost fertility, which seems to be based on the opinion of one fertility nutritionist.
Although a healthy balanced diet containing fresh fruit and vegetables has many health benefits and may improve sperm quality, this is not a basis for reports that raspberries boost fertility.
Proven ways that men can boost their fertility include:
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.