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Polyunsaturted fats and cataracts

IHN logo Age-related cataracts are very common in elderly people and are the leading cause of blindness in the world. They cause cloudiness in the lens of the eye, which can be corrected surgically, but at a large social and medical cost. A team of researchers at Tufts University has investigated some of the ways in which dietary fat is related to lens cell membrane composition and function. They gathered data from 440 women aged 53 to 73 years. The participants were recruited from the Nurses' Health Study in 1976. Over the next 10 to 15 years, the women's intake of polyunsaturated fats (PUFAs) was measured five times. PUFAs consist of omega-6 and omega-3 fats; both generally considered healthy elements of the diet. Omega-3 fats are present in flax seed and canola oils, and fish oils. Omega-6 fats are found in most common vegetable oils such as safflower, sunflower, corn and soy oils. Of all the fatty acids found in foods, only two, linoleic acid (LA) and alpha- linolenic acid (ALA), cannot be made in the body and thus are essential. However, small amounts are adequate to avoid deficiency. LA and ALA are present in the lens membrane, and may become oxidized, so high concentrations could lead to free radical damage and cloudiness in the lens.

The researchers found an increased risk of developing cataracts when long-term intake of either LA or ALA was increased. Women in the highest quartile for LA and ALA intake were at more than double the risk of developing a cataract. This link applied to age-related nuclear cataracts, the most common type, but not to cortical or subcapsular cataracts. The researchers noted that the average intake of linoleic acid was almost 10 times the intake of alpha-linolenic acid; they surmise that linoleic acid may be the major culprit in cataract formation, but suggest that further study is needed to clarify the relation between dietary fat and cataract risk. Previous findings also indicate that a high intake of omega-6 fats can be damaging to health, and suggest that the ratio of omega-6 to omega-3 fats needs to be kept low. Experts also point out that early humans would not have had access to the liquid vegetable oils that are so widely available today.
Lu, M et al. Dietary fat intake and early age-related lens opacities. American Journal of Clinical Nutrition, Vol. 81, April 2005, pp. 773-779

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