The research, led by M C Cosgrove of Unilever, used data from the first National Health and Nutrition Examination Survey (NHANES I) to examine the relationship between dietary nutrient intakes and skin-ageing appearance. The study suggests that higher intakes of vitamin C and linoleic acid, and lower intakes of fats and carbohydrates are associated with better skin in older age, providing further support for the growing number of beauty foods and nutricosmetics. Although the investigation concentrates on dietary intakes of nutrients and not supplements, it shows significant relationships between a number of nutrients and skin ageing even when controlled for other factors. According to the researchers, studies on supplements often concentrate on multi ingredient supplements therefore it can be difficult to determine which nutrient is having an effect. Furthermore, supplement studies concentrate on short term courses of high dose nutrients. Cosgrove and the team claim that this examination is the first to concentrate on daily nutrient intake, rather than supplements. NHANES I was conducted by the National Center for Health Statistics in the US between 1971 and 1974, on a nationwide sample of over 30 000 individuals. Information collected includes dietary assessment, height and weight measurements, supplement intake, physical activity level, and sunlight exposure. In addition, clinical examinations were conducted by dermatologists and skin-ageing appearance was defined as having a wrinkled appearance, senile dryness (dryness as a result of aging) and skin atrophy (skin thinning). In total 4025 females between the ages of 40 and 74 were included in the study. Researchers found that relationships existed between certain nutrient intakes and skin ageing appearance independent of factors such as age, race, energy intake, education, sunlight exposure, family income, menopausal status, BMI, supplement use and physical activity. In particular, lower intakes of vitamin C in the diet were significantly associated with the prevalence of wrinkled appearance and senile dryness. The researchers hypothesise that this is due the vitamin's antioxidant properties, the role it plays in collagen synthesis and its postulated photoprotective qualities. In addition, the study suggests that a higher dietary intake of linoleic acid has a beneficial role in reducing the chances of developing senile dryness and skin atrophy. According to researchers the association between linoleic acid and skin ageing has not been investigated but they suggest a similar photoprotective effect might play a role, in addition to the fact that low intake of linoleic acid can lead to dermatitis with marked abnormalities. Furthermore, the study found that higher intakes of fats and carbohydrates were associated with increased chances of wrinkled skin appearance and skin atrophy. The researchers suggest that emphasising the positive effect that healthy eating may have on the skin, particular aging skin, may motivate people to improve their diets, along with providing persuasive evidence for the beneficial qualities of certain nutrients. The NHANES data is generally believed to have good measures of many factors such as age, race and socio economic status, meaning that researchers can control for these factors when interpreting results. However, the use of facial cosmetics was not measured. Although the use of facial cosmetics is unlikely to be affected by nutrient intake, the team conclude that a potential confounding effect cannot be ruled out.