Plasma Insulin-Like Growth Factor I Levels in the Elderly: Relation to Plasma Dehydroepiandrosterone Sulfate Levels, Nutritional Status, Health and Mortality

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Abstract
Background: Insulin-like growth factor I (IGF-I) has beneficial metabolic effects. Because plasma IGF-I levels have been reported to be enhanced by dehydroepiandrosterone (DHEA) administration, it has been suggested that the IGF-I may be implicated in some of the reported associations between low DHEA sulfate (DHEAS) levels and impaired health measures in elderly subjects. The nutritional status, which also regulates plasma IGF-I levels, is also an important determinant of health outcome. Objective: We sought to investigate the associations between plasma IGF-I levels and plasma DHEAS levels, nutritional status, health, and mortality in the elderly. Methods: In 256 community-dwelling subjects aged 65–101 years, enrolled in the Paquid study, a health questionnaire was used to acertain their functional disabilities, any history of medical disorders, self-perceived health, depressive symptoms, and their cognitive function. Biological measurements included levels of plasma IGF-I, albumin, transthyretin, and DHEAS. Mortality data were available for 6 years following blood sampling. Results: In this elderly population with no impairment in nutritional status, the plasma IGF-I levels decreased significantly with age (p = 0.02). The plasma IGF-I levels correlated positively with those of transthyretin (p = 0.0001). IGF-I also correlated with DHEAS (p = 0.04), but the correlation did not remain significant after adjustment for age. As opposed to SDHEA, the plasma IGF-I levels did not correlate with the results from the health questionnaire. The baseline IGF-I values in the highest tertile were associated with a higher risk of short-term mortality than those in the lowest tertile (RR = 8.4 at 2 years, p = 0.007). Conclusions: Our results suggest that IGF-I is not connected with the association between low plasma DHEAS levels and the impaired results from the health questionnaire. The relationship between plasma IGF-I highest levels and mortality should be further explored.