A woman's diet at the time of conception might cause lasting changes in the DNA of her children, potentially influencing their development, researchers say.
In a new study, researchers analyzed the diets of women in rural parts of The Gambia, in western Africa, who experience major changes in their diets over the course of each year as the area goes through rainy seasons and dry seasons.
"The rainy season is often referred to as 'the hungry season,' and the dry season 'the harvest season,'" said study author Robert Waterland, a nutritional epigeneticist at Baylor College of Medicine in Houston. "During the rainy season, villagers have a lot more farming labor to do, and they gradually run out of food collected from the previous harvest."
Yearlong staples of the women's diet include rice, a grain called millet, peanuts and cassava. But during the rainy season, they eat more leafy green vegetables similar to spinach, which are very high in folate, a nutrient that is especially important during pregnancy.
The scientists investigated the concentration of nutrients in the blood of 84 pregnant women who conceived at the peak of the rainy season and 83 women who conceived at the peak of the dry season. In addition, they analyzed the DNA of six specific genes in the women's infants when they were 2 to 8 months old. [7 Ways Pregnant Women Affect Babies]
The researchers found that in all six genes, the infants who were conceived during the rainy season had consistently higher rates of "methylation" in their DNA. A methylation is a change made to DNA — it's the addition of methyl groups to the DNA strand, a so-called epigenetic modification to DNA — and is a process that can silence the expression of a gene.
Methylation generally depends on nutrients such as folate, choline, methionine, and vitamins B2 and B6, the researchers said. In the study, methylation in the infants' genes was linked to various nutrient levels in the mother's blood.
"Our results represent the first demonstration in humans that a mother's nutritional well-being at the time of conception can change how her child's genes will be interpreted, with a lifelong impact," senior study author Branwen Hennig, of the London School of Hygiene & Tropical Medicine, said in a statement.
Prior studies in animals had suggested that environmental influences before conception might lead to epigenetic changes in the offspring. For instance, a 2003 study revealed a female mouse's diet can alter the color of her offspring's coat by permanently modifying DNA methylation.
"These specific epigenetic marks on DNA are very stable — essentially permanent, as far as we know," Waterland said.
Past research suggested environmental influences could have epigenetic effects during development in humans as well. For instance, whether Dutch women suffered through post-World War II famines during pregnancy apparently influenced how skinny or fat their children were later in life.
However, there was little strong evidence that environmental factors could trigger permanent changes to DNA throughout the human body, Waterland said.
"It's also important to note that their diet wasn't the only thing that changed — there was more physical activity due to farm labor during the rainy season, which contributed to weight loss during the rainy season and regaining of weight during the dry season," Waterland said. "Such changes contribute to what nutrients are circulating within the women."
In the new study, a nearly identical epigenetic effect was found in both blood and hair-follicle DNA of the infants. "This suggests all the cells in these kids' bodies have the same mark associated with their season of conception," Waterland said.
The long-term consequences of these epigenetic effects in children remain unknown. "We want to develop a catalog of all regions in the human genome that can get altered epigenetically by diet," Waterland said. "This will help give us the ability to tell what the likely role such changes might have in disease, and what particular diseases might be most likely to have an epigenetic component."
"Our ultimate goal is to define an optimal diet for mothers-to-be that would prevent defects in the methylation process," study author Andrew Prentice, of the London School of Hygiene & Tropical Medicine, said in a statement. "Preconceptional folic acid is already used to prevent defects in embryos. Now our research is pointing towards the need for a cocktail of nutrients, which could come from the diet or from supplements."
The scientists detailed their findings online today (April 29) in the journal Nature Communications.
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