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the extracellular matrix of the joint and collagen proteins. Children of parents with early onset osteoarthritis are at higher risk of developing it themselves compared with families where this is not the case (reviewed in Loughlin16). Obesity This is the strongest modifiable risk factor. Three to six times the body weight is transferred across the knee joint during walking. Any increase in weight should be multiplied by this factor to estimate the excess force across the knee joint when an overweight patient walks. The Chingford Study showed that for every two unit increase in body mass index (approximately 5 kg), the odds ratio for developing radiographic knee osteoarthritis increased by 1.36.17 Increasing weight increased the risk of contralateral osteoarthritis of the knee in women with established osteoarthritis of one knee. Being overweight at an average age of 36–37 is a risk factor for developing knee osteoarthritis in later life (>70 years of age). Losing 5 kg of weight reduced the risk of symptomatic knee osteoarthritis in women of average height by 50%.9 Also, increased risk of developing progressive osteoarthritis seems to be apparent in overweight people with localised disease.13 Diet People in the lower tertile of vitamin C and vitamin D blood levels had a threefold risk of progression of knee osteoarthritis.7 The antioxidant and collagen promoting properties of vitamin C may be of benefit as animal models have shown vitamin C may delay the onset of osteoarthritis. Vitamin D intake and status had no effect on development of knee osteoarthritis but those with low intake and low serum levels had an increased risk of osteoarthritis knee progression. Vitamin E has not been shown to be of benefit.