A team from the University of North Carolina at Chapel Hill found that for every additional tenth of a part per million of selenium in volunteers' bodies, there was a 15-20 per cent decrease in their risk of knee osteoarthritis.
The work, based on data gathered from 940 participants, is thought to be the first to link the trace mineral to joint health. Arthritis severity was directly related to how low selenium levels were.
"Our results suggest that we might be able to prevent or delay osteoarthritis of the knees and possibly other joints in some people if they are not getting enough selenium," said study leader Dr Joanne Jordan.
The findings, to be presented in San Diego tomorrow at the annual meeting of the American College of Rheumatology, could be particularly important for populations in Europe. Research published in 2002 revealed that selenium levels in British bread-making wheats are 10 to 50 times lower than in their American or Canadian counterparts, owing to reduced levels of the mineral in UK soil and lower pollution. Daily intake of the mineral is therefore often lower than the recommended amount in Britain.
At the same time, incidence of osteoarthritis is rising in most developed countries in conjunction with an ageing population and obesity, a major risk factor for osteoarthritis of the knee. The UK currently has the eighth highest obesity rate in the world. In the past year, more than 2 million Britons visited their GP because of osteoarthritis.
The US team first suspected that selenium might play a role in preventing osteoarthritis after observing that in severely selenium-deficient areas of China, people frequently develop Kashin-Beck disease, which causes joint problems relatively early in life.
They selected pariticipants in the major Johnston County Osteoarthritis Project, and divided them into three groups based on the selenium levels measured in toenail clippings.
Those with the highest selenium levels faced a 40 per cent lower risk of knee osteoarthritis than those in the lowest-selenium group.
"Those in the highest selenium group had only about half the chance of severe osteoarthritis or disease in both knees. Some of the findings were even stronger in African-Americans and women," said Jordan.
She added that there appears to be a clear relationship between selenium and osteoarthritis. The mechanism behind this link needs to be further investigated in the laboratory but the researchers believe the mineral might act as a protective antioxidant.
"Later, we'll want to expand the study with larger samples and see whether selenium supplementation reduces pain or other symptoms," added Jordan.