Ninety healthy adults, aged between 18 and 50, and who live in the greater Dunedin area, are taking part in the double-blind study, which starts next month.
Vitamin D is made in the body when it is exposed to sunlight.
Low levels of vitamin D have been linked with bone fractures, heart disease, high blood pressure and diabetes, study organisers said.
Participants in the six-month-long study will take either supplements comprising 1000 international units of vitamin D2, or vitamin D3, or will take a placebo, in a control group.
Five blood tests will also be taken, from the end of summer and during the winter, to clarify some uncertainty about which form of vitamin D is more effective in lifting vitamin D levels in the body, including the blood.
The significant role of vitamin D in calcium absorption and metabolism for bone health was well known, organisers said.
There was also growing evidence that adequate vitamin D status might also help prevent autoimmune diseases, hypertension and various types of cancer.
Most recent national surveys showed that more than 40% of New Zealand children and adults had an insufficiency of vitamin D.
Dr Lisa Houghton, a lecturer in the Otago human nutrition department, is the Dunedin study's principal investigator, and departmental head Prof Murray Skeaff is a co-investigator, with Meredith Rose, an assistant research fellow, undertaking much of the work.
Dr Houghton said the study, backed by a $29,300 Laurenson Award, had been carefully designed to clarify which form of supplement was most effective.
Prof Skeaff said there was already "huge public interest in vitamin D, myself included".
"If we find D2 is not as good, D3 should be used. There remains some uncertainty and we're trying to bring some clarity to this question," Prof Skeaff said.
The only way to improve vitamin D nutrition effectively and safely was by increased fortification of vitamin D in the food supply and/or dietary supplements, organisers said.
Factors contributing to vitamin D insufficiency included inadequate dietary intake of the vitamin, and seasonal variation in ultraviolet-B radiation. Few foods contained vitamin D, and the main source was synthesis in the skin arising from sunlight exposure. Increasing this sunlight-related production was not advised because of concerns about an increased risk of skin cancer, study organisers said.
