Organic produce and meat typically isn't any better for you than conventional food when it comes to vitamin and nutrient content, although it does generally reduce exposure to pesticides and antibiotic-resistant bacteria, according to a US study.

“People choose to buy organic foods for many different reasons. One of them is perceived health benefits,” said Crystal Smith-Spangler, who led a team of researchers from Stanford University and the Veterans Affairs Palo Alto Health Care.

“Our patients, our families ask about, 'Well, are there health reasons to choose organic food in terms of nutritional content or human health outcomes?'”

She and her colleagues reviewed more than 200 studies that compared either the health of people who ate organic or conventional foods or, more commonly, nutrient and contaminant levels in the foods themselves.

The foods included organic and non-organic fruits, vegetables, grains, meat, poultry eggs and milk.

According to US Department of Agriculture standards, organic farms have to avoid the use of synthetic pesticides and fertilisers, hormones and antibiotics. Organic livestock must also have access to pastures during grazing season.

Many of the studies used, though, didn't specify their standards for what constituted “organic” food, which can cost as much as twice what conventional food costs, the researchers wrote in the Annals of Internal Medicine.

Smith-Spangler and her colleagues found there was no difference in the amount of vitamins in plant or animal products produced organically and conventionally – and the only nutrient difference was slightly more phosphorous in the organic products.

Organic milk and chicken may also contain more omega-3 fatty acids, but that was based on only a few studies.

More than one third of conventional produce had detectable pesticide residues, compared with seven per cent of organic produce samples. Organic pork and chicken were 33 per cent less likely to carry bacteria resistant to three or more antibiotics than conventionally produced meat.

Smith-Spangler told Reuters Health it was uncommon for either organic or conventional foods to exceed the allowable limits for pesticides, so it was not clear whether a difference in residues would have an effect on health.

But others said more research is needed to fully explore the potential health and safety differences between organic and conventional foods, and it was premature to say organic foods aren't any healthier than non-organic versions.

“Right now I think it's all based on anecdotal evidence,” said Chensheng Lu, who studies environmental health and exposure at the Harvard School of Public Health.