Description

EATING rice bran - a "superfood" - may increase exposure to the carcinogen arsenic. The news is particularly worrying as the bran is given to malnourished children in poor countries as a food supplement.

Arsenic occurs naturally in groundwater as a result of minerals leaching from rocks. Although found in varying amounts in drinking water around the world, including in the US, Australia and China, these countries have limits on how much can be present based on World Health Organization (WHO) guidelines. In Bangladesh, where people are exposed to very high levels, the problem is more serious.

The toxic metal also gets taken up by plants grown in contaminated water, including rice. Despite this, only China has up-to-date standards for safe amounts of arsenic in food.

Previously, Andrew Meharg of the University of Aberdeen, UK, and colleagues showed that in areas where arsenic is present, brown rice contains more arsenic than "polished" white rice, in which the outer bran has been removed. Now a team led by Meharg has polished brown rice from China and Bangladesh, allowing them to separate and analyse the bran. They found that it contained four times as much arsenic as brown rice and six times as much as white rice, suggesting that arsenic is concentrated in the bran.

This sounds like good news - the bran is usually discarded. But in recent years, a number of rice bran products, rich in vitamins and fibre, have come onto the market, mainly targeted at health-food consumers.

Meharg purchased nine of these products online, made in the US and in Japan. All were found to contain between 0.48 and 1.16 milligrams of arsenic per kilogram, which exceeds China's legal limit of 0.15 mg/kg (Environmental Science and Technology, DOI: 10.1021/es801238p). Four of the products are "rice bran solubles", which can be mixed with water to make a drink. At least two of these - both made by Nutracea of Phoenix, Arizona - are distributed to children in the developing world.

So how dangerous is it to eat rice bran? Meharg says these arsenic-containing rice bran solubles are "inappropriate for use in food-aid programmes". Indeed, the risk of skin, lung, bladder and kidney cancer increases with arsenic intake, leading toxicologists to say that there is no "safe" limit.

But such risks must be weighed against the benefits of the foods. Nutracea has distributed rice bran solubles to 67,000 pre-school children in Guatemala, and monitored the nutritional state of 150 of them. At the start, 37 per cent were deemed malnourished, but that dropped to just 5 per cent after taking 15 grams of solubles, five days a week for six months.

As New Scientist went to press, Nutracea had not responded to a request for comment.

Marie Vahter, an environmental toxicologist at the Karolinska Institute in Stockholm, Sweden, believes the benefits of consuming tainted bran do not outweigh the risks. Her own studies suggest that children are particularly susceptible to the effects of arsenic.

"One would expect dietary supplements to be virtually free of unwanted substances like arsenic - especially when aimed at children," adds Philippe Grandjean of the Harvard School of Public Health.

The WHO told New Scientist: "We are looking for and are open to new evidence about the toxicity of chemicals that are important for public health, and obviously arsenic is one of these."