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Abstract

This study determined if 6-weeks vitamin D2 supplementation (vitD2, 3800 IU/day) had an influence on muscle function, eccentric exercise-induced muscle damage (EIMD), and delayed onset of muscle soreness (DOMS) in National Association for Stock Car Auto Racing (NASCAR) NASCAR pit crew athletes. Subjects were randomized to vitD2 (n = 13) and placebo (n = 15), and ingested supplements (double-blind) for six weeks. Blood samples were collected and muscle function tests conducted pre- and post-study (leg-back and hand grip dynamometer strength tests, body weight bench press to exhaustion, vertical jump, 30-s Wingate test). Post-study, subjects engaged in 90 min eccentric-based exercise, with blood samples and DOMS ratings obtained immediately after and 1- and 2-days post-exercise. Six weeks vitD2 increased serum 25(OH)D2 456% and decreased 25(OH)D3 21% versus placebo (p < 0.001, p = 0.036, respectively), with no influence on muscle function test scores. The post-study eccentric exercise bout induced EIMD and DOMS, with higher muscle damage biomarkers measured in vitD2 compared to placebo (myoglobin 252%, 122% increase, respectively, p = 0.001; creatine phosphokinase 24 h post-exercise, 169%, 32%, p < 0.001), with no differences for DOMS. In summary, 6-weeks vitD2 (3800 IU/day) significantly increased 25(OH)D2 and decreased 25(OH)D3, had no effect on muscle function tests, and amplified muscle damage markers in NASCAR pit crew athletes following eccentric exercise.

1. Introduction

Limited evidence suggests that treatment of vitamin D insufficient athletes may improve performance [,]. In the UK, 5000 IU/day vitamin D3 supplementation for eight weeks improved 10 m sprint times and vertical jump performance in athletes who started the study with a mean serum 25(OH)D level of 12 ng/mL []. Maintaining adequate vitamin D status may also reduce inflammation and aid in recovery from injury or intensive workouts, but data in humans are inconsistent [,]. One study showed that vitamin D3-treated rats experienced attenuation in plasma creatine kinase (CK) and inflammation biomarkers following high-intensity exercise, with an increase in muscle VDR protein expression []. No previous human study has been published regarding the effect of vitamin D supplementation in countering eccentric exercise-induced muscle damage (EIMD) and delayed onset of muscle soreness (DOMS). We hypothesized that 6-weeks supplementation with vitamin D (3800 IU/day) using vitamin D2 Portobello mushroom powder would improve muscle function and strength, and attenuate EIMD and DOMS in NASCAR pit crew athletes during their off-season in December and January.

2.4. Supplement

Fresh Portobello mushrooms (Agaricus bisporus) were air dried at 71–76 °C for 48–72 h in a convection dryer []. Once dried, the mushrooms pieces were milled to approximately 35 mesh, or 500 µm. The powder was then treated on a vibrating conveyor with pulsed light (UVB) from a Xenon broad spectrum lamp (100–800 nm) operating at 3 pulses per second for a total of thirty 2 ms pulses which converted ergosterol to ergocalciferol (vitamin D2). Subjects were given Portobello mushroom powder with or without vitamin D2 mixed in soymilk powder (non-vitamin D fortified) in six plastic containers (one for each week of the study). Subjects ingested one level teaspoon of the product each day (with or without 3800 IU vitamin D2) during breakfast.

3. Results

Total serum 25(OH)D was 43.7 ± 2.7 and 39.6 ± 1.6 ng/mL in the placebo and vitamin D groups, respectively, during October, 40.7 ± 2.1 and 36.6 ± 1.7 ng/mL in December (pre-supplementation), and 38.6 ± 1.8 and 37.4 ± 1.9 ng/mL in January (post-supplementation) (time effect p = 0.001, interaction effect p = 0.238). Supplementation with mushroom vitamin D2 powder for 6 weeks caused no significant change in 25(OH)D (p = 0.127), a significant increase in serum 25(OH)D2 (8.14 ± 1.96 ng/mL, p < 0.001) and a significant decrease in serum 25(OH)D3 (−7.48 ± 2.28 ng/mL, p = 0.036) compared to placebo (0.076 ± 1.19 ng/mL and −2.11 ± 1.09 ng/mL, respectively) (A,B). Serum 25(OH)D3 was highest in October and then decreased to levels measured in December and January in the placebo group (within group contrasts, p < 0.01).

3. Results

The post-study eccentric training bout caused significant increases in serum myoglobin (), LDH (), CK (), and DOMS () (all time effects, p < 0.001). Significantly higher post-exercise serum levels for myoglobin and CK were measured in the vitamin D2 compared to placebo group (both interaction effects, p < 0.001), with a trend for higher serum LDH levels (interaction effect, p = 0.065). The pattern of change in DOMS did not differ between groups (interaction effect, p = 0.490). For the whole group, change in serum 25(OH)D2 correlated significantly with change in post-exercise serum myoglobin (r = 0.57, p = 0.001).

4. Discussion

Contrary to our hypothesis, high-dose vitamin D2 supplementation in NASCAR pit-crew athletes during a 6-week period in December and January amplified EIMD and had no effect on muscle function. Vitamin D2 supplementation increased serum 25(OH)D2 ~8 ng/mL but decreased serum 25(OH)D3 ~7.5 ng/mL, with no significant change in total 25(OH)D.

Abstract

Mushroom irradiation has been considered a sustainable process to generate high amounts of vitamin D2 due to the role of this vitamin for human health and of the global concerns regarding its deficient or inadequate intake. Mushrooms are also receiving increasing interest due to their nutritional and medicinal properties. However, there is still a knowledge gap regarding the effect of UV irradiation on mushroom bioactive compounds. In this study, two of the most cultivated mushroom species worldwide, Agaricus bisporus and Pleurotus ostreatus, were irradiated with UV-B, and the effect of processing was investigated on the contents of vitamin D2 as well as on antioxidant and antiglycation activities. UV irradiation increased vitamin D2 up to 57 µg/g d.w, which is an adequate level for the fortification of a number of target foods. UV irradiation decreased the antioxidant activity when measured by the Folin–Ciocalteu reagent, the 2,2-diphenyl-1-(2,4,6 trinitrophenyl) hydrazyl radical assay and the ferric ion-reducing antioxidant power assay, but did not decrease the mushroom’s ability to inhibit glycation of a target protein. These results open up a new area of investigation aimed at selecting mushroom species with high nutraceutical benefits for irradiation in order to maintain their potential properties to inhibit oxidative and glycation processes responsible for human diseases.

2.2. Mushrooms

P. ostreatus and A. bisporus were purchased from the market. The irradiation treatment was performed as described previously []. In brief, about 10 kg of body fruits were used for each mushroom type, cut into 4 mm slices, spread on an oven rack in a single layer and air-dried at 37 °C for 48 h. During the first 24 h of air-drying, the mushrooms were irradiated using two fluorescent lamps installed at 30 cm above the mushroom layer. In accordance to most of the previous studies so far performed [,], a UV-B source was chosen for the irradiation. The lamps delivered a UV-B (280–315 nm) irradiance of 0.4 W/m2. At the end of the process, about 1 kg of dried mushroom was obtained from each mushroom type and the product was grinded to a fine powder using a Thermomix TM 31 (Vorwerk Contempora S.r.l., Milan, Italy). Control P. ostreatus and A. bisporus powders were obtained by processing mushrooms with the same drying and grinding procedure without UV irradiation.

3.1. The Effect of Mushroom Irradiation on Vitamin D2 Content

Initial content of vitamin D2 was low in both commercial mushrooms considered. This result is consistent with previous studies and could be associated with the conditions used for industrial cultivation of mushrooms that generally occurs with low exposure to sunlight [,]. UV irradiation led to an increase in vitamin D2 content from 3.1 to 37 µg/g d.w. and from 0.3 to 57 µg/g d.w. in P. ostreatus and A. bisporus, respectively (). The initial contents of ergosterol were 3600 and 5700 µg/g d.w. in P. ostreatus and A. bisporus, respectively (). These values fall in the range previously reported [] and remained high after the generation of significant amounts of vitamin D2. This result may suggest that upon UV irradiation. the residual amount of ergosterol is still relevant for drug development and could contribute to the health-promoting effects of mushrooms [].