Vitamin D status and biomarkers of inflammation in runners.

BACKGROUND AND PURPOSE: The extra-skeletal functions of vitamin D - including its role in inflammatory modulation - are now well recognized but have not yet been investigated in an athletic population. Thus, the purpose of this study was to investigate the relationship between vitamin D status and pro- and anti-inflammatory cytokines (as markers of inflammation and immune system function) in endurance athletes. PATIENTS AND METHODS: We analyzed fasting blood samples from 19 healthy, endurance-trained male and female runners (following a standardized diet and exercise regimen) for vitamin D status (serum 25-hydroxyvitamin D [25(OH)D)] and specific plasma cytokine concentrations (tumor necrosis factor alpha [TNF-α], interferon-gamma [IFN-γ], interleukin [IL]-4, and IL-10). Serum/plasma concentrations were log-transformed and simple regression analysis was used to determine significant associations between 25(OH)D and cytokine concentrations. RESULTS: Forty-two percent of participants had insufficient vitamin D status [25(OH)D< 32 ng/mL], whereas 11% were deficient [25(OH)D < 20 ng/mL]. TNF-α and IL-4 were variable, ranging from 2.9 to 36.4 pg/mL and 0 to 252.1 pg/mL, respectively. Concentrations of IFN-γ and IL-10 were minimal, with means of 6.7 ± 7.0 pg/mL and 4.8 ± 5.1 pg/mL, respectively. Regression analysis revealed a significant inverse association between 25(OH)D and TNF-α concentrations (R(2) = 56.5, P < 0.001) but not between 25(OH)D and the remaining cytokines, IFN-γ, IL-4, and IL-10 (P = 0.477, 0.694, and 0.673, respectively). CONCLUSION: These results call further attention to the epidemic of vitamin D insufficiency, even in outdoor athletes, and support a possible link between decreased vitamin D status and one particular marker of inflammation. Future investigations are necessary to determine whether increased inflammation in athletes with reduced vitamin D status could increase risk for inflammation-related injury.

Vitamin D and athletes.

While it is well recognized that vitamin D is necessary for optimal bone health, emerging evidence is finding that adequate vitamin D intake reduces risk for conditions such as stress fracture, total body inflammation, infectious illness, and impaired muscle function. Studies in athletes have found that vitamin D status is variable and is dependent on outdoor training time (during peak sunlight), skin color, and geographic location. Although research has found that athletes generally do not meet the U.S. dietary reference intake for vitamin D, inadequate endogenous synthesis is the most probable reason for insufficient/deficient status. Given the recent findings, it is imperative that sports dietitians and physicians routinely assess vitamin D status and make recommendations to help athletes achieve a serum 25(OH)D concentration of >or=32 and preferably >or=40 ng.mL(-1). Further research is needed to determine the effect of vitamin D status on injury, training, and performance in athletes.

Effect of honey versus sucrose on appetite, appetite-regulating hormones, and postmeal thermogenesis.

OBJECTIVE: Increased per capita consumption of sweeteners may be responsible in part for the rising prevalence of obesity in the United States. Recent studies suggest that consumption of honey is not associated with this same obesogenic effect and may have beneficial effects neuro on body weight. The purpose of this study was to evaluate whether the meal-induced responses of ghrelin and peptide YY(3-36) (PYY(3-36)) and/or meal-induced thermogenesis differ following a honey- versus a sucrose-containing meal. METHODS: In a double-blind randomly assigned study, appetite hormones (ghrelin, PYY(3-36), leptin) and glycemic and thermic responses were evaluated following isoglucidic ∼450 kcal honey- or sucrose-containing breakfasts in 14 healthy, nonobese women (22 ± 3 y). Blood samples and hunger ratings were obtained at baseline and every 30 minutes for 240 minutes following the meal. Meal-induced thermogenesis was measured by indirect calorimetry. Ad libitum food intake was evaluated from a free-choice meal following the test meal. RESULTS: Honey consumption delayed the postprandial ghrelin response (p = 0.037), enhanced the total PYY (p = 0.007) response, and blunted the glucose response (p = 0.039) compared with consumption of the sucrose-containing meal. Meal-induced insulin response, hunger ratings, thermogenesis, and subsequent ad libitum food intake, however, did not differ (p > 0.10) between diet treatments. CONCLUSIONS: Alterations in meal-induced responses of ghrelin and PYY(3-36) but not meal-induced thermogenesis may be responsible in part for the potential "obesity protective" effect(s) of honey consumption. A blunted glycemic response may be beneficial for reducing glucose intolerance. Further research is required to determine if these findings hold true for obese individuals, for males, or with habitual consumption.

Effects of endurance running and dietary fat on circulating ghrelin and peptide YY.

Ghrelin and peptide YY (PYY) are newly recognized gut peptides involved in appetite regulation. Plasma ghrelin concentrations are elevated in fasting and suppressed following a meal, while PYY concentrations are suppressed in fasting and elevated postprandially. We determine whether ghrelin and PYY are altered by a low-fat, high-carbohydrate (10% fat, 75% carbohydrate) or moderate-fat, moderate-carbohydrate (35% fat, 50% carbohydrate) diet and; whether these peptides are affected by intense endurance running (which is likely to temporarily suppress appetite). Twenty-one endurance-trained runners followed a controlled diet (25% fat) and training regimen for 3 days before consuming the low-fat or isoenergetic moderate-fat diet for another 3 days in random cross-over fashion. On day 7 runners underwent glycogen restoration and then completed a 90-minute pre-loaded 10-km time trial on day 8, following a control breakfast. Blood samples were obtained on days 4 and 7 (fasting), and day 8 (non-fasting) before and after exercise for analysis of ghrelin, PYY, insulin and growth hormone (GH). Insulin, GH, Ghrelin and PYY changed significantly over time (p < 0.0001) but were not influenced by diet. Ghrelin was elevated during fasting (days 4 and 7), while insulin and PYY were suppressed. Following the pre-exercise meal, ghrelin was suppressed ~17% and insulin and PYY were elevated ~157 and ~40%, respectively, relative to fasting (day 7). Following exercise, PYY, ghrelin, and GH were significantly (p < 0.0001) increased by ~11, ~16 and ~813%, respectively. The noted disruption in the typical inverse relationship between ghrelin and PYY following exercise suggests that interaction of these peptides may be at least partially responsible for post-exercise appetite suppression. These peptides do not appear to be influenced by dietary fat intake.

Should we be concerned about the vitamin D status of athletes?

A surprisingly high prevalence of vitamin D insufficiency and deficiency has recently been reported worldwide. Although very little is known about vitamin D status among athletes, a few studies suggest that poor vitamin D status is also a problem in athletic populations. It is well recognized that vitamin D is necessary for optimal bone health, but emerging evidence is finding that vitamin D deficiency increases the risk of autoimmune diseases and nonskeletal chronic diseases and can also have a profound effect on human immunity, inflammation, and muscle function (in the elderly). Thus, it is likely that compromised vitamin D status can affect an athlete's overall health and ability to train (i.e., by affecting bone health, innate immunity, and exercise-related immunity and inflammation). Although further research in this area is needed, it is important that sports nutritionists assess vitamin D (as well as calcium) intake and make appropriate recommendations that will help athletes achieve adequate vitamin D status: serum 25(OH)D of at least 75 or 80 nmol/L. These recommendations can include regular safe sun exposure (twice a week between the hours of 10 a.m. and 3 p.m. on the arms and legs for 5-30 min, depending on season, latitude, and skin pigmentation) or dietary supplementation with 1,000-2,000 IU vitamin D3 per day. Although this is significantly higher than what is currently considered the adequate intake, recent research demonstrates these levels to be safe and possibly necessary to maintain adequate 25(OH)D concentrations.