Sarcopenia, a condition characterized by loss of skeletal muscle mass and strength with aging, is considered a key factor in the disablement process. It is widely recognized that age-related sarcopenia is caused by a combination of intrinsic factors involving changes at the energetic molecular and cellular levels, and extrinsic or environmental factors such as nutrition and exercise.

Most studies looking at carotenoid intake or circulating levels and their relation with physical function have been cross-sectional. Thus, it is not known whether deficiency of carotenoids is a significant predictor of accelerated functional loss, or simply reflects a global deterioration of functional status, with little or no effect on the risk of losing physical function.

To address the hypothesis that low serum carotenoids may predict a greater decline in skeletal muscle strength, we examined the relationship between plasma total carotenoids at enrollment and the decline in hip, knee and grip muscle strength over a six-year interval among participants in the InCHIANTI study, a population-based study of older adult living in the Chianti region of Tuscany, Italy.

Subjects and Methods

The study participants consisted of men and women, aged 65 and older, who participated in the Invecchiare in Chianti, “Aging in the Chianti Area” (InCHIANTI) study, conducted in two small towns in Tuscany, Italy (www.inchiantistudy.net). Briefly, in August 1998, 1270 people aged 65 years and older were randomly selected from the population registry of Greve in Chianti and Bagno a Ripoli. The participants were seen again for a three-year followup visit (2001-2003) and a six-year follow-up visit (2004-2006). Aliquots of serum and plasma were immediately obtained and stored at -80° C. Aliquots of plasma were shipped on dry ice to Dr. Semba’s laboratory for measurements of plasma carotenoids. Carotenoids were measured using high performance liquid chromatography (HPLC). Total carotenoids were calculated as the sum of alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin, and lycopene in Ìmol/L.

Results

Of the 1155 participants ≥65 years seen at enrollment, 1055 (91.3%) participated in the blood drawing. There were 948 (82.1%) participants at enrollment that had both plasma carotenoids and at least one of the three measures of strength (hip, knee, and/or grip strength) available for this analysis. There were 628 participants who had measurements of muscle strength conducted at the 6-year follow-up visit. Of 328 people who were not seen at the 6-year follow-up visit, 179 had died, 122 refused to participate, and 14 moved out of the study area. Between enrollment and the 6-year follow-up visit, the overall mean declines (SD) in hip strength, knee strength and grip strength were -2.28 (5.24) kg (P <0.0001), -0.82 (5.60) kg (P <0.0001) and -1.44 kg (P <0.0001), respectively.

Adjusting for age, sex, education, body mass index, WHR, calf muscle density, CSAM, current smoking, total energy intake and physical activity, participants in the lowest quartile of total plasma carotenoids were at higher risk of developing poor hip strength (OR = 3.01; 95% CI: 1.44-6.31, P = 0.003), knee strength (OR = 2.94; 95% CI: 1.41-6.12, P = 0.004) and grip strength (OR = 1.87; 95% CI: 0.97-3.63, P = 0.07) compared to those in the highest quartile.

Discussion

This study shows that older community-dwelling men and women with low plasma carotenoid concentrations experience a greater decline in hip, knee and grip muscle strength over a period of six years compared to those with high plasma carotenoids. These findings support and expand the results of previous cross-sectional studies that showed low carotenoid intake and serum level of carotenoids, natural antioxidants, are independent correlates of poor skeletal muscle strength and impaired physical performance. In particular, our longitudinal analysis shows that older community-dwelling men and women with a total plasma carotenoids less than 1.37 Ìmol/L are at a higher risk of a decline in skeletal muscle strength over time.