Effects of vitamin D and quercetin, alone and in combination, on cardiorespiratory fitness and muscle function in physically active male adults

Abstract

IntroductionVitamin D and the antioxidant quercetin, are promising agents for improving physical performance because of their possible beneficial effects on muscular strength and cardiorespiratory fitness.PurposeThe purpose of this study was to determine the effects of increased intakes of vitamin D, quercetin, and their combination on antioxidant status, the steroid hormone regulators of muscle function, and measures of physical performance in apparently healthy male adults engaged in moderate-to-vigorous-intensity exercise training.MethodsA total of 40 adult male participants were randomized to either 4,000 IU vitamin D/d, 1,000 mg/d quercetin, vitamin D plus quercetin, or placebo for 8 weeks. Measures of cardiorespiratory fitness and muscle function, blood markers for antioxidant and vitamin D status, and hormones 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and testosterone were measured pre- and postsupplementation.ResultsAt enrollment, 88.6% of participants were vitamin D sufficient (serum 25-hydroxyvitamin D >50 nmol/L) and had normal serum testosterone levels. Supplementation with vitamin D significantly increased serum 25(OH)D concentration (by 87.3% in the vitamin D group, P<0.001) and was associated with an increasing trend of testosterone concentration. There were no changes in concentration of 1,25(OH)2D3 and markers of antioxidant status associated with vitamin D or quercetin supplementation. No improvements in physical performance measures associated with vitamin D and quercetin supplementation were found.ConclusionThe findings obtained demonstrate that long-term vitamin D and quercetin supplementation, alone or in combination, does not improve physical performance in male adults with adequate vitamin D, testosterone, and antioxidant status.

The effect of vitamin D supplementation on the androgenic profile in men: A systematic review and meta‐analysis of clinical trials

“…All the eight studies conducted for meta‐analysis were published in English and were double‐blind RCTs. However, two of the double‐blind studies were factorial design (Saha & Goswami, ; Scholten et al, ). All the trials were published from 2008 to 2018.…”

“…Change in TT concentration after vitamin D supplementation was assessed in eight studies containing 10 effect sizes with 1,061 participants (Heijboer et al, ; Jorde et al, ; Lerchbaum et al, ; Lerchbaum et al, ; Pilz et al, ; Saha & Goswami, ; Scholten et al, ; Zittermann et al, ). The overall effect of meta‐analysis showed no significant effect of vitamin D on TT (WMD = 0.20, 95% CI: −0.20, 0.60, p = 0.336), and heterogeneity ( I 2 = 0.0%, p = 0.508) was not observed among the studies (Figure ).…”

Safety Aspects of the Use of Quercetin as a Dietary Supplement

“…The intake of antioxidative compounds such as vitamin C may theoretically mask the suggested pro‐oxidative effects of quercetin. In human intervention studies, pro‐oxidative effects of quercetin were not found with quercetin doses at 500–1000 mg d –1 applied for 3–12 weeks ( n Q = 6–333), but it is still an open question whether quercetin may exhibit pro‐oxidative effects in the human body, especially after a long‐term use of high quercetin doses …”

“…The intake of antioxidative compounds such as vitamin C may theoretically mask the suggested pro-oxidative effects of quercetin. In human intervention studies, pro-oxidative effects of quercetin were not found with quercetin doses at 500-1000 mg d -1 applied for 3-12 weeks (n Q = 6-333), [55][56][57][58][59] but it is still an open question whether quercetin may exhibit pro-oxidative effects in the human body, especially after a long-term use of high quercetin doses. [30,60,61] In general, oral intake of quercetin in humans seems to be well tolerated and only a very low incidence of adverse effects has been observed to date (for details see Supporting Information Table S1).…”

“…In humans, one intervention study with young healthy men (mean age of around 30 years) did not reveal an impact of quercetin on testosterone levels in plasma after intake of 1000 mg quercetin per day for 8 weeks. [57] To date, no other human studies examining an influence of quercetin on hormone levels or on parameters related to male reproduction (spermatogenesis) have been identified. The absence of studies extending beyond 8 weeks makes it difficult to conclude on any long-term effects of quercetin on the reproductive system in men.…”