Vitamin D levels within New Zealand athletes, in relation to body fat
Background: Recent research has found a high prevalence of vitamin D deficiency and insufficiency in both the general New Zealand population as well as within athletic populations. Vitamin D has a role in calcium regulation and is therefore important for bone mineralisation as well as having a role in muscle strength. Further research has linked deficiency and insufficiency with many diseases, including osteomalacia and myopathy. Within the general New Zealand population 32% were found below the New Zealand Ministry of Health recommended level of 50nmol/L and of that 4.9% were deficient (less than 25nmol/L). Limited studies have been undertaken within athletic populations, of those studies a high prevalence of deficiency and insufficiency was noted which could have a large effect on performance. No studies of vitamin D levels within New Zealand athletes have been published. There are also limited studies investigating the association between vitamin D and body fat in athletic populations. Athletic populations generally have body fat levels substantially lower than the general population, as body fat is the main storage site of vitamin D this may affect storage capacity. It is important to investigate the vitamin D levels in the New Zealand athletic population to determine the risk of deficiency or insufficiency. Objective: To describe the vitamin D levels of New Zealand athletes in relation to body fat. Methods: The present study tested 72 elite New Zealand athletes who volunteered to participate in the study at both a Summer and Winter testing. Ethnicity, gender and sport were reported for each athlete as well as dietary and supplemental intake at the Summer testing. Vitamin D levels were taken at both Summer and Winter via fingerprick blood samples which were analysed for 25(OH)D using Enzyme immunoassay. Skinfold thickness measurements were carried out on all 72 athletes in Summer but only 61 athletes in Winter. Results: Total vitamin D mean (SD) was 109.2 (24.3) nmol/L in Summer and 88.9 (19.3) nmol/L in Winter (p<0.001). None of the athletes were found to have levels below 50 nmol/L at either the Summer or Winter testing. There was a significant inverse relationship between skinfolds and vitamin D in Summer (p=0.002, r2=-0.103) and a significant weak negative association in Winter (p=0.015, r2=-0.003). Food and supplemental intake was found to have no association with vitamin D levels. Conclusion: No athletes had vitamin D levels below the Ministry of Health recommended level of 50nmol/L at either the Summer or Winter testing, whereas previous athletic studies have found a high prevalence below this level. Studies have suggested an optimal level of 75nmol/L of which not all athletes within our study met. This proposed optimal level requires further research within the athletic population to ensure optimal performance. An inverse relationship between vitamin D and body fat was found, meaning those athletes with higher body fat measurements were found to have lower vitamin D levels.
Advisor: Black, Katherine
Degree Name: Master of Dietetics
Degree Discipline: Human Nutrition
Publisher: University of Otago
Keywords: Vitamin D; Athletes; New Zealand; fat
Research Type: Thesis