Vitamin D and adult bone health in Australia and New Zealand: a position statement

To the Editor: We read with alarm the extraordinary statements in the position statement on vitamin D and adult bone health published recently in the Journal.1 The suggestion that “it is a fallacy that Australians receive adequate vitamin D from casual exposure to sunlight” is not true.

The suggested basis for this statement is an extraordinary extrapolation from a single study in which a small number of volunteers had whole body exposure on one occasion for 10–15 minutes to midday summer sun in Boston. It is not possible to extrapolate in such a way from this single demonstration, as the effect of shorter exposure times or repeated daily exposures were not examined. In fact, a study in Australia showed that the adult population (including those aged over 70 years) received sufficient sunlight while using sunscreen to ensure that no-one was found to have vitamin D deficiency during the study period.2

While it is well accepted that ultraviolet B (UVB) radiation is essential for the formation of vitamin D3 in the skin, it is equally well established that continued exposure of vitamin D to UVB radiation results in its degradation. Hence, the importance of knowing the effect of lower sun exposures on vitamin D production.

It is intriguing that the authors of the position statement recommended a daily sun exposure dose that they calculate will produce 1000 IU of vitamin D, but, if sun exposure is not possible, a vitamin D supplement of at least 400 IU per day.

The high prevalence of vitamin D deficiency among institutionalised older Australians is a tragedy, but this cannot be used as the basis of advice for the general population who do receive daily sun exposure and appear to be the target of the statement. Nor can the mild vitamin D deficiency found in a single study in southern Victoria be used to recommend sun exposure in more northern Australian climes. Finally, while vitamin D supplementation has been shown to reduce the risk of fractures in the elderly, the proposed beneficial effect of deliberate sun exposure has not been demonstrated.

Recently, a joint position statement was approved by the Australian and New Zealand Bone and Mineral Society, Osteoporosis Australia, the Australasian College of Dermatologists and the Cancer Council Australia. This included the statement that “The majority of Australians generally have sufficient ultraviolet radiation exposure to enable adequate vitamin D production . . . to form and maintain healthy, strong bones”.3 This statement, endorsed only a few weeks ago, is in obvious conflict with the position statement from the same organisations that was published in this Journal. The latter puts the vast majority of Australians at further risk of skin cancers, which are already epidemic in our country.4