A recent Sunday Star Times article highlighted national concerns that inner-city apartment living, with children playing mainly indoors, could cause a rise in the number who were vitamin D deficient.
The principal of one Auckland school said that up to half of its more than 400 pupils lived in apartments and many had little or no access to outside recreational areas.
The most well-known illness resulting from vitamin D deficiency is rickets, a childhood disease marked by stunted growth and ill-formed bones.
Dunedin City Council city development manager Dr Anna Johnson said yesterday there was also a trend in Dunedin towards increased inner-city apartment living, but relatively few children were living in such apartments.
The cost of transport, and the lengthy commuting times required to reach inner-city jobs from the outlying suburbs, particularly when both parents worked, were drivers for the apartment trend in northern cities. But these were clearly not such significant factors in Dunedin, Dr Johnson said.
Prof Merriman said it was unclear exactly what effect the trend towards inner-city apartment living in Dunedin and elsewhere was having on vitamin D levels.
However, many trends, individually not necessarily of great significance, if combined were likely to result in some people not getting enough vitamin D.
Now, more people worked indoors, rather than in outdoor jobs and vitamin D deficiency was "prevalent as a result of our modern lifestyle". Also, many young people watched television and played computer games rather than playing outdoors.
Vitamin D was a hormone manufactured in the body and one step in its manufacture required "the input of UV-B rays from the sun".
Some vitamin D could be obtained from the diet - oily fish, eggs, milk - but not enough to satisfy daily requirements.
Some limited sun exposure, combined with wearing hats and avoiding sunburn, was needed to generate sufficient vitamin D, he said. During winter in Dunedin, vitamin D supplementation was probably required.
More research was needed and some parts of the "scientific puzzle" involving vitamin D were still missing.
But more recently, vitamin D deficiency had been strongly implicated in several diseases, including childhood (type 1) diabetes and adult (type 2) diabetes, multiple sclerosis, cancer (colon, breast, prostate, lung, skin), heart disease and infectious diseases.
Vitamin D was also a "cofactor for the balance of the immune system, helping it to do what it evolved to do - fight infections and cancers - and keeping it from getting up to mischief", he said.
Prof Murray Skeaff, of the Otago University human nutrition department, said skin cancer rates in Australia and New Zealand were the highest in the world and Cancer Society guidelines should be complied with.
Views varied on the ideal levels of vitamin D. Two recent national surveys had shown that New Zealand adults and children averaged about 50 nanomoles of vitamin D per litre of blood and he was not convinced there was an immediate "crisis" requiring much higher vitamin D levels, he said.
