Tuesday March 31 2015
Pesticides may affect the shape and number of sperm
"Pesticides on fruit and vegetables may be damaging sperm counts and men should consider going organic if they want to have children," The Daily Telegraph reports.
A study found men who ate the highest amount of fruit and vegetables with high levels of pesticides had a 49% lower sperm count, as well as a 32% lower count of normally formed sperm, than men who consumed the least amount. Sperm can sometimes be an abnormal shape, making it harder for them to move and fertilise an egg.
The results of this study should be viewed with caution. Researchers did not assess individual diets for pesticide residues. They also did not know if the food the men ate was grown organically or conventionally (a failing The Telegraph overlooked).
So it is possible the men's dietary exposure to pesticides was misclassified. The men in the study were all attending fertility clinics, so the results may not apply to the general population.
The study certainly should not be seen as an invitation to avoid eating fruit and vegetables. Aside from the general health harms a fruit and veg-free diet would hold, this could also negatively impact your sperm quality.
Many factors can affect men's sperm count and quality, including whether they smoke or drink alcohol, as well as how much exercise they take and their weight. Whether or not pesticide residue found in our diet is another factor that affects sperm quality is an important topic that needs further study.
Where did the story come from?
The study was carried out by researchers from the Harvard T H Chan School of Public Health, Massachusetts General Hospital, Brigham and Women's Hospital, and Harvard Medical School in the US.
It was funded by the National Institute for Environmental Health Sciences, the National Institutes of Health, and the Ruth L Kirschstein National Research Service Award.
The study was published in the peer-reviewed journal Human Reproduction on an open-access basis, so it is free to read online.
The study was covered uncritically by most of the UK media. The Telegraph's assertion that, "Men who eat fruit and vegetables with high pesticide residues could double their sperm count by switching to organic food" was highly misleading.
The study did not compare the effects of organic and non-organic food on sperm count. However, both The Telegraph and the Mail Online included comments from UK experts.
What kind of research was this?
This was a cohort study exploring whether the consumption of fruits and vegetables with high levels of pesticide residues is linked to lower semen quality.
This type of study cannot prove cause and effect, as other factors could be causing any effects seen. However, in studies of this type, researchers try to take account of other factors that can affect a health outcome.
In this case, for example, male fertility is known to be affected by lifestyle factors such as smoking and weight, which were taken into account in the statistical analyses.
The researchers say in nearly one-third of couples seeking help with conception the problem is one of male infertility.
They say occupational exposure to pesticides has been linked to lower sperm counts, and argue that pesticide exposure may explain a general decline in semen quality. Whether pesticide exposure through diet could affect male fertility is unknown.
What did the research involve?
Men attending a fertility clinic filled out food frequency questionnaires from which the researchers estimated their intake of pesticides from fruit and vegetables. The results were then analysed to look for an association between higher pesticide consumption and lower sperm counts.
Researchers used an ongoing study of couples attending a US fertility clinic. The men in the study had to be aged between 18 and 55 without any history of vasectomy, and be in a couple seeking fertility treatment with their own eggs and sperm.
Between 2007 and 2012, the male partners in sub-fertile couples (couples who require medical assistance to conceive) completed a food frequency questionnaire. They were asked how often on average they consumed specified amounts of fruit and vegetables over the previous year using standard portion sizes.
The fruit and vegetables were categorised as being high, moderate or low in pesticide residues based on data from the annual United States Department of Agriculture Pesticide Data Program.
Fruit or vegetables low in pesticide residues included peas, beans, grapefruit and onions. Those with high residues included peppers, spinach, strawberries, apples and pears. This data takes account of how food has been prepared, such as whether it has to be peeled.
By this criteria, 14 of the fruits and vegetables in the questionnaire were categorised as high in pesticide residues and 21 as low-to-moderate in pesticide residues.
The researchers divided the men into four groups, ranging from those who ate the greatest amount of fruit and vegetables high in pesticide residues (1.5 servings or more per day), to those who ate the least amount (less than half a serving per day).
They also categorised whether men ate a "prudent" diet – consisting of high intakes of fish, chicken, fruit, vegetables and wholegrains – or a "Western pattern" – high intakes of red and processed meat, butter, high-fat dairy, refined grains, snacks, high-energy drinks, mayonnaise and sweets.
Semen samples were also collected from the men over an 18-month period following their dietary assessment. Both sperm count and the size and shape of the sperm and whether they moved normally were evaluated by computer-aided semen analysis (CASA).
A total of 338 semen samples collected from 155 men between 2007 and 2012 were used in the analysis. Fifty-seven men contributed one sample, 51 men provided two samples, and 47 provided three or more semen samples.
Using statistical methods, the researchers analysed the association between pesticide intake from fruit and vegetables with sperm count and quality.
They adjusted their findings for other factors known to affect male fertility, such as age, smoking status, weight, periods of sexual abstinence, exercise, dietary patterns, and history of varicose veins (variocele) in the testicles.
What were the basic results?
The researchers found that:
- the men's total fruit and vegetable intake was unrelated to their semen quality
- high pesticide residue fruit and vegetable intake was associated with poorer semen quality
- on average, men in the highest quartile of high pesticide residue fruit and vegetable intake, with 1.5 or more servings a day, had a 49% (95% confidence interval [CI] 31 to 63) lower total sperm count and a 32% (95% CI 7 to 58) lower percentage of normally shaped sperm than men in the lowest quartile of intake (0.5 servings a day)
How did the researchers interpret the results?
The researchers say their findings suggest that exposure to pesticides used in agriculture through diet may be sufficient to affect the quality and amount of sperm in humans.
Whether pesticide exposure in the diet is linked to male fertility problems is an important issue, but, as the authors point out, there are several reasons to view the results of this trial with caution:
- the men were all attending a fertility clinic with their partner, so some of them will have had fertility issues unrelated to their diet or lifestyle
- they used national surveillance data, rather than looking at individual diets, to assess how much pesticide residue the men had consumed
- they did not have information on whether the men were eating organic or non-organic food
- the men had to remember and report on their diet over the previous year, which could affect the reliability
- their diets were only assessed once, which might have led to misclassification, and diets could change over time
Male fertility can be affected by several factors. Although the researchers tried to adjust their findings for these, it is always possible that both measured and unmeasured confounders affected the results. Further studies looking at this important topic are needed.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.