In the first study, researchers at the Harvard School of Public Health evaluated the dietary intake of specific nutrients for more than 85,000 women and more than 42,000 men, in data supplied over 18 years for the women and over 12 years for the men.

They report in January's issue of Diabetes Care that the men and women whose diets included the largest amounts of magnesium were the least likely to develop type 2 diabetes. The research also showed that most of the participants in the studies consumed magnesium through foods, such as wholegrains, nuts and green leafy vegetables; less than 5 per cent of those followed took magnesium supplements.

A second study of nearly 40,000 women, also by researchers at Harvard (in conjunction with researchers at Brigham and Women's Hospital in Boston), found that overweight women who consumed large amounts of magnesium were 22 per cent less likely to develop type 2 diabetes than those who consumed lower amounts of dietary magnesium.

The researchers concluded that people at increased risk for diabetes should eat a diet high in magnesium-rich foods. An editorial in the journal supports these conclusions and calls for a randomized prospective clinical trial to explore this issue further. The mineral has also been associated with a reduced risk of coronary heart disease.

Last week we reported on new research revealing a positive association between vitamin D intake and reduced risk of diabetes. In 2002, 18.2 million people or 6.3 per cent of the US population, were diagnosed with diabetes. Cases of type 2 diabetes are going up as the numbers of obese grow.