Vitamin D update
Date: 2014-03-07
Author: - Editor
Access: Public

An objective way to assess vitamin D status is through measuring the circulating 25 hydroxy-vitamin D concentration. Concentrations of less than 20–25 nmol/L reflect severe vitamin D deficiency, whereas concentrations of between 25 -40 nmol/L indicate bordering vitamin D deficiency. Vitamin D deficiency often results in reduced bone mineral density, and can also influence muscle metabolism and cause muscle weakness. Vitamin D supplementation may prevent osteomalacia. In epidemiological terms, the benefits of supplementation are realized in prevention of osteoporosis progression. There is also some speculation that the prevalence of some forms of cancer, hypertension and multiple sclerosis may be influenced by vitamin D status.

Most research has focused on supplementing individuals with vitamin D deficiency with lower doses rather than periodic use of single high doses. Since 2010 two randomised controlled studies have been published that investigated the use of single annual high dose Vitamin D supplementation. The results were not necessarily as expected, as there was a finding of an increase in fractures and falls amongst the elderly.

The British ‘Wessex’ study (4 354 men, 5086 women) investigating the benefits of use of a yearly 300 000 IU vitamin D2 single injection dose to reduce fractures actually revealed an increase in risk of hip or femur fracture (hazard ratio = 1.49, 95 % CI 1.02–2.18) compared to the control group. Analysis of female subjects with male subjects showed that Vitamin D treatment increased the risk of any non-vertebral fracture, however there was no associated risk in males.

Earlier, an Australian study investigating the effects of an annual single Vitamin D dose (500 000IU) in preventing falls and fractures in women aged 70 years and older (n=2256) and showed that there was an increased risk of falls and fractures in the three months after treatment, relative to the control group.

Current Australian recommendations of high dosing in severe deficiency are 10 000 to 50 000IU colecalciferol, weekly for 6 weeks rather than one large annual dose. Alternative lower dosing schedules of Vitamin D in severe deficiency include:

• 3000-5000IU daily for at least 6-12 weeks followed by maintenance dosing of 1000IU daily

• 50 000IU once per month for 3-6months followed by 1000IU daily maintenance dose.

Commonly seen maximal doses of Vitamin D within South Australia tend to average between 50 000 IU every month or 100 000 IU administered on a three monthly basis.

To date, no further studies have investigated the potential risk associated with high annual doses of Vitamin D with respect to the potential for increasing the risk of falls and fractures. When treating severe Vitamin D deficiency, further research is required to elucidate the optimal dosing regimen, as there are no comparative studies between high dose annual administration and other current recommendations.

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