Vitamin D is identified as one of the key regulators of calcium and phosphate homeo-stasis, which makes it essential during bone turnover (Holick et al. , 2011). Furthermore, vitamin D contributes extensively in mineral resorption and is essential to mineral retention (Burke, 2015). Severe Vitamin D deficiency (<200 IU) is heavily associated with bone disorders such as rickets in children and osteomalacia in adults (Litman, Ulstrom and Westin, 1957).
Epidemiological evidence indicates that groups which are less likely to achieve sufficient levels of vitamin D, such as the elderly people and dark-skinned people living in non-tropical environments, are more likely to suffer with osteomalacia (Bates et al. , 2003). This evidence has prompted committees such as the Institute of Medicine, Food, and Nutrition board (1997) to advocate higher intake targets in certain pop-ulations. However, it is highly possible any bone-related disorders that are significant within these groups can be attributed to wider lifestyle, biological, and hereditary factors.
Dore (1983) suggested epidemiological evidence is poor indicator of cause and effect in multifactorial disorders. Thus, more clinical evidence is requ-ired to confirm such effects. Strong associations have been reported in some studies reviewing the effects of 25-hydroxyvitamin D on fracture prevalence. Peac-ock et al. (2000) reported a 29% reduction in hip fractures and a 24% reduction in non-vertebrae fractures, when comparing vitamin D intake trials against placebo groups.
In addition, Holick et al. (2011) observed a significant reduction in vertebrae fractures whilst reviewing an elderly cohort, supplementing vitamin D during a longitudinal study. However, wider factors have also demonstrated an effect on fracture prev-alence, specifically in populations such as the elderly (Rizzoli et al. , 2009). Thus, fracture rates cannot confirm the effectiveness of vitamin D, more clinical research is required. Research revising the effects of vitamin D on BMD is inconsistent.
Silk, Greene, and Baker (2015) found, when measuring males across multiple measurement sites, there was little evidence to support high vitamin D intake. In a sample of 867 participants the greatest increase of BMD was 0. 64% at a single site (hip). Whist some participants displayed minor increases of BMD, the overall effect size was limited. Furthermore, increases of BMD where only observed in older males, whom already had lower than average measurements.
Reid, Bolland, Grey (2014) conducted a meta-analysis, on current vitamin D trials across numerous measurement sites on predominantly female samples. They found increases of approximately 2% across the sample, however, similarly to the males, the minor effects were typically observed in older participants with already compromised BMD. Thus, there is some evidence that supports positive effects of vitamin D in older adults with already compromised BMD, this however, was not reflected across the rest of the population.
Some research has identified that children and adolescents that regularly consume the RDA for calcium and vitamin D, have greater BMD readings at the hip and lumbar section of the spine (Heaney, 2003). In addition, Lamberg-allardt et al. (2001) observed increased BMD and peak bone mass in adolescents who consumed > 400 IU of vitamin D. Such findings are important because bone capital accumulation acquired earlier in life, has demonstrated a relative effect on peak bones mass during adulthood (Brown et al. 1999).
Similarly to the previous research, the overall effect size of vitamin D trials is small, however, the evidence base supporting the effect of vitamin D in children and adolescents is relatively consistent. Holick et al. (2006) concludes that there is an acceptable evidence base to support the requirements for vitamin D intake in children and adolescent, for purposes of skeletal health and growth. Taken together, there is some evidence to suggest consuming >400 IU of vitamin D could result in reduced bone accretion.
In addition, there is a strong evidence body associating adequate vitamin D consumption with reduced fracture risk. Thus, consuming over >400 may be advisable. However, the evidence linking vitamin D and BMD is inconsistent. Studies reviewing the effects of vitamin D on BMD indicated that the observable effects were minimal, although they were more significant in elderly individuals. Studies reviewing adolescents were more conclusive, and thus, consuming an adequate amount can be considered more important to this population.