This study aimed to examine the association between serum antioxidants and muscle strength among older individuals. Researchers hypothesized that higher serum carotenoids, vitamin E, and retinol would increase muscle strength.

With age comes muscle weakness loss, which increases mortality risk, falls and fractures are more likely to occur, and daily activities can be less successful. A decrease in strength can be caused by various factors, including changes in eating patterns, anabolic resistance, comorbidities, decreased physical activity, and increased oxidative stress.

A substance with antioxidant properties could decrease oxidative stress, maintaining muscle strength over time. This is because increased oxidative stress is one of the causes of muscle weakness in older adults. For example, vitamin E, carotenoids, and retinol are potent antioxidants that can decrease oxidative stress and enhance muscle strength.

A study by Semba et al. showed that higher plasma levels of carotenoids and tocopherol are associated with stronger grips, hips and knees in older women. Using a prospective cohort study, Sahni et al. found a positive association between intake of total carotenoids, lycopene, lutein and zeaxanthin and handgrip strength.

Results of the Study

The experts performed a cross-sectional study evaluating 1172 individuals (627 men and 545 women) who participated in the 2002 NHANES survey. Carotenoids (α-carotene, trans-β-carotene, cis-β-carotene, lutein/zeaxanthin combination, trans-lycopene), vitamin E, and retinol levels were determined by high-performance liquid chromatography.

The researchers used a 24-hour food recall to assess dietary intake. In NHANES 2001, dietary intake was assessed via 4-step multiple passes, while for NHANES 2002, the US Department of Agriculture (USDA) experts used an automated five-pass method.

The isokinetic knee extension test evaluated muscle strength. The association between serum antioxidant levels and strength was assessed using linear regression, adjusted for confounders (energy intake, protein intake, body mass index, gender, age, C-reactive protein, ethnicity, marital status, annual income, educational level, physical activity, smoking, hypertension, arthritis, and diabetes).

“The explanation as to why only serum α-carotene (but not all the other antioxidants) was associated with strength in the present study is not fully clear, but can be related to the antioxidant action promoted by α-carotene,” the researchers explained.

It has been suggested that α-carotene may have a greater potential antioxidant effect than β-carotene, despite being chemically similar to α-carotene. According to an in vivo study, α-carotene inhibits neuroblastoma cell proliferation by about ten times more than β-carotene.

Furthermore, vegetables with high beta-carotene content, such as dark green and yellow-orange vegetables, were associated with a lower lung cancer risk than all other vegetables.

A recent study shows that serum levels of beta-carotene have an inverse relationship with death rates from various causes. Collectively, beta-carotene appears to have a greater antioxidant effect compared with other types of carotenoids.

There was a positive association between muscle strength and alpha-carotene levels (p-trend = 0.027). However, power was not related to vitamin E, carotenoids, and retinol serum levels. Serum α-carotene, but not different antioxidants, was positively associated with muscle strength in older adults.

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