Clare Hughes, London

Researchers at St Thomas's Hospital and King's College London have shown that silicon, found in abundance in beer, increases bone mineralisation in men and premenopausal women. Students who drink beer can continue their favourite pastime, safe in the knowledge that it could be doing them good; beer increases bone strength.

The researchers looked at dietary silicon intake and found that beer was the biggest single contributor of silicon. Dr Jonathan Powell, senior lecturer in nutrition and medicine, said, "Drinking half a pint of beer a day provides about 6 mg of silicon--that's about 20% of our daily dietary intake." He added that silicon intake is greater in men than women and decreases with age.

In conjunction with researchers at Harvard and Tufts Universities in Boston, United States, the team looked at the association between dietary silicon intake and bone mineral density using the Framingham offspring cohort. They reported their findings at a recent meeting in Brussels.

Postmenopausal women were the only people who did not respond to the silicon. This is probably because the bone formation associated with silicon is counteracted by the normal physiological reduction in bone density seen with ageing, especially in postmenopausal women.

Silicon is thought to aid bone maturation by helping to bring collagen molecules together allowing them to form cross links. Powell said, "Peak bone mass is reached by 35 years, and low bone mass is a risk factor for osteoporosis in later life. It could be argued that silicon would be most beneficial in younger people working towards peak bone mass."

Silicon in beer and other fluids, such as mineral water, is found in its readily absorbable form, orthosilicic acid. In solid foods, the silicon is polymerised and needs to be hydrolysed in the gut lumen before it can be absorbed. As a result about one and a half times as much silicon is absorbed from fluids compared with solids. About 55% is absorbed from beer compared with an average of 35% from other foods.

Dr Martin Hodson of Oxford Brookes University said, "Silicon is found in the husks of barley, which surround the grain. Normally we wouldn't eat the husks but in beer making these are mashed as part of the process, so releasing soluble silicon into the beer."

Beer only has a positive effect on bones, however, when drunk in moderation. Excessive alcohol consumption can lead to an increase in bone fractures, by reducing osteoblast function, and has negative effects on other body systems. Powell said, "Peak benefit would come from drinking one to three units a day. As always, people should drink only in moderation." Other sources of dietary silicon include water, cereal products such as rice and wholemeal bread, green beans, and dried fruit.