The study is the work of scientists at the University of California (UC), Berkeley, and the Lawrence Berkeley National Laboratory, and is published in the 19th March issue of the journal Human Reproduction.
Women of childbearing age are encouraged to maintain a healthy intake of folate because it is essential for healthy fetal development, and to prevent neural tube birth defects such as spina bifida or anencephaly (severe type of brain damage). That is why folic acid is now added to bread, cereal, flour and other grain products in the US.
But this is the first study to suggest that folate intake in men may affect their children.
Researcher at UC Berkeley's School of Public Health and coordinator of the study, Suzanne Young, said:
"Recent studies have suggested that paternal diet affects sperm count and motility, which is important for conception, but this new study takes it further to say that male diet may be important for healthy offspring as well."
Young said their study was the first to examine the effects of diet on chromosomal abnormalities in sperm.
"These abnormalities would cause either miscarriages or children with genetic syndromes if the sperm fertilized an egg," explained Young.
The researchers said that about 1 to 4 per cent of healthy male sperm has an abnormal number of chromosomes, or aneuploidy. These abnormalities arise when cells divide (meiosis) in the testis, but their cause is not well understood.
If an aneuploidic sperm fertilizes a normal egg, the fetus would either miscarry or develop a chromosomal disorder, such as trisomy, where cells have three copies of each chromosome instead of the more usual two (one from each parent).
In this study the investigators looked at three chromosomes linked with common types of aneuploidy in live births: X, Y and chromosome 21. Down syndrome, for example, is caused by having an extra chromosome 21. Klinefelter syndrome, which can affect language and learning development, is caused by an extra X chromosome in boys, and boys carrying an extra Y chromosome have XYY syndrome, also linked to learning and behavioral difficulties.
The participants were 97 non-smoking men with no previous history of reproductive or fertility problems. The aged from 22 to 80 and were either still working at or had retired from a government research laboratory.
The men filled in questionnaires about their diet and supplements like multi-vitamins and other nutrients. Semen samples were taken up to a week later.
After taking out the effects of age, alcohol and medical history, the results showed that men who reported the highest folate intake had a 19 per cent lower rate of aneuploidic sperm that men with moderate folate intake, and 20 per cent lower than men with the lowest folate intake.
The analysis did not show any links between aneuploidy and other nutrients such as zinc, calcium, beta-carotene and other vitamins, said the researchers, who concluded that:
"Men with high folate intake had lower overall frequencies of several types of aneuploid sperm."
Co-principal investigator of the study, professor of epidemiology and maternal and child health at UC Berkeley's School of Public Health, Brenda Eskenazi, said:
""The emphasis related to the birth of a healthy baby has been weighted towards the health and diet of women, not just during pregnancy, but before."
"What we're finding now is that a nutritious diet, specifically folate intake, may be beneficial for men as well when it comes to producing healthy offspring," she added.
Folate, which occurs naturally in a range of foods such as liver, leafy green vegetables, peas, beans, lentils and citrus fruits, is a water soluble vitamin of the B group.
Folate is essential for DNA, RNA and protein synthesis and the development of new cells. It also helps to control homocysteine, an amino acid that has been linked to heart disease.
But before men hoping to become dads rush out to buy folic acid or start maxing out on lentils, they should take note, as the researchers themselves suggested, that this study only found a link between folate and healthy sperm, it did not establish for certain that there is a cause and effect relationship.
Study co-principal investigator and chair of the Radiation Biosciences Department at Lawrence Berkeley National Laboratory, Andrew Wyrobek, cautioned:
"We can't yet say that increasing folate in your diet will lead to healthier sperm."
"But we did come up with enough evidence to justify a larger, clinical and pharmacological trial in men to examine the causal relationships between dietary folate levels and chromosomal abnormalities in their sperm," added Wyrobek.
This information will help us set dietary folate levels that may reduce the risk of miscarriage or birth defects linked to the fathers," he said.
If further research supports these findings, the researchers suggest it might be a good idea to increase the current recommended 400 micrograms daily allowance of folate for men hoping to become dads.
"The association of folate, zinc and antioxidant intake with sperm aneuploidy in healthy non-smoking men."
S.S. Young, B. Eskenazi, F.M. Marchetti, G. Block, and A.J. Wyrobek.
Hum. Reprod. Advance Access published on March 19, 2008.
Click here for Abstract.
Sources: Journal abstract, press statement from University of California,Berkeley.