Low Serum Vitamin D Levels Are Associated with Reduced Muscle Strength in Women with Breast Cancer

Vitamin D insufficiency has been frequent in women with breast cancer (BC), as well as impaired muscle strength (MS), and a possible relationship between these conditions has been investigated in different populations, except in women with BC. This study aimed to analyze the association between serum vitamin D levels and MS in women with BC. Observational cross-sectional study carried out with adult women with BC, without metastasis/recurrence, with up to 12 months of diagnosis. Serum 25(OH)D concentration was categorized as insufficient (<30 ng/mL) or sufficient (≥30 ng/mL). MS was assessed by the Handgrip Strength test and divided into strength tertiles of the population itself: 1st tertile (6-21 kg), 2nd tertile (22-26 kg), and 3rd tertile (27-39 kg). Adjusted multinomial logistic regression models verified the association of serum vitamin D levels in MS tertiles, with a significance of 5%. A total of 151 women were evaluated. Most women had insufficient levels of vitamin D (70%). Insufficient serum vitamin D levels were associated with the 1st and 2nd tertile of MS (odds ratio [OR]: 5.74, 95% confidence interval [CI]: 1.77-18.64, <i>P</i> = 0.004; OR: 4.48, 95% CI: 1.34-14.97, <i>P</i> = 0.015, respectively). Serum vitamin D insufficiency incresed the probability to present lower tertiles of MS in women with BC.