Vitamin D insufficiency in adolescent males in Southern Tasmania: prevalence, determinants, and relationship to bone turnover markers

Abstract

There are limited data on vitamin D insufficiency in healthy children. The aim of this study was to describe the prevalence and determinants of vitamin D insufficiency and its association with bone turnover in adolescent boys (N = 136, mean age 16 years). Sun exposure and physical activity were assessed by questionnaire. Vitamin D stores were assessed by serum 25-hydroxyvitamin D3 (25[OH]D3). Bone turnover was assessed by bone-specific alkaline phosphatase (BAP) and urinary pyridinoline (PYR) to creatinine (Cr) ratio (mmol PYR/micromol Cr). The mean 25(OH)D3 level was low (44 nmol/l; 68% < 50 nmol/l; range, 16-87) and was associated with self-reported sun exposure on winter weekends (r = 0.23, p = 0.01), school holidays (r = 0.22, p = 0.01), and weekdays (r = 0.17, p = 0.05). It was also associated with number of sports (r = 0.34, p < 0.001) and vigorous activity (r = 0.22, p = 0.01) but not television, computer, and video watching (r = -0.04, p = 0.68). In multivariate analysis, number of sports but not total sun exposure remained significantly associated with 25(OH)D3. Furthermore, 25(OH)D3 was significantly associated with BAP in cutpoint analysis (cutpoint 55 nmol/l, p = 0.03) but not continuous analysis (r = -0.12, p = 0.16) and PYR in both forms (r = -0.23, p = 0.01, cutpoint 43 nmol/l, p = 0.01). In conclusion, vitamin D insufficiency is common in healthy adolescent boys in winter in our setting, is primarily derived from sports-related sun exposure, and is associated with bone turnover markers. These data suggest that a 25(OH)D3 level of at least 43-55 nmol/l is required for optimal bone health in children.

Validity and Reliability of Adult Recall of Past Sun Exposure in a Case-Control Study of Multiple Sclerosis

“…Two Tasmanian studies of 8-year-old (19) and adolescent (20) children found that serum 25(OH)D was correlated with usual levels of sun exposure in the season preceding the measurements [r = 0.20, P < 0.01 (19) and r = 0.23, P = 0.01 (20) for exposure during school holidays; r = 0.16, P = 0.02 (19) and r = 0.23, P = 0.01 (20) for exposure during weekends]. Lifetime sun exposure in adults measured by a calendar method was associated with actinic damage in the study by English et al (8).…”

“…Three validity studies have been conducted in school children (18)(19)(20), showing that these children are able to recall recent and current habitual sun exposure. In adolescents, polysulfone badge recordings of UVR exposure on 4 weekend days in late spring correlated well with two questions on habitual sun exposure (correlation 0.35 for time in the sun, 0.29 for activities outside; ref.…”

“…18). In 8-year-old (19) and adolescent (20) children, recent sun exposure was associated with levels of serum 25(OH)D. In adults, current sun exposure recorded in a diary has been shown to correlate with personal UVR dosimeters (18,21), and lifetime sun exposure has been associated with actinic damage (8). Two studies assessed the reproducibility of recall of childhood and adolescent sun exposure by adults (8,22).…”

Adverse interaction of low-calcium diet and low 25(OH)D levels on lumbar spine mineralization in late-pubertal girls

“…(13) Serum 25(OH)D levels are considered the best marker of vitamin D status and have been used commonly to assess the prevalence of vitamin D deficiency/insufficiency in healthy children and adolescents. (9,10,(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26) However, a clear understanding of the biologic significance of given concentrations of circulating 25(OH)D is still lacking, and reference ranges for vitamin D are being reassessed on the basis of what constitutes a normal concentration compared with optimal concentrations. (27)(28)(29) Most clinicians agree that serum 25(OH)D levels below 25 to 30 nmol/L (10 to 12 ng/mL) may lead to nutritional rickets, hypocalcemic convulsions, dental problems, and poor growth in children and adolescents.…”

Vitamin D Intake and Cardiometabolic Risk Factors in Adolescents

“…It is reported that in healthy Caucasian adolescent boys aged 16-18 years, there was a significant association between sports-related sun exposure and vitamin D status. 41 Additionally, a study of Chinese girls aged 15 years also observed that lifestyle factors, such as participation in organized sports and time spent exercising, both at school and in leisure time, showed significant and independent positive association with 25(OH)D concentration. 42 This can be explained by the fact that most exercise by these subjects was taken outdoors, so that their higher vitamin D status may have resulted from an increased exposure to sunlight.…”