Breast cancer is about twice as likely in New Zealand women than in those living closer to the equator, an Australian study has found.
The Westmead Breast Cancer Institute study, to be presented at a conference in Sydney tonight, also analysed the geographical occurrences of melanoma - and found the opposite.
The researchers found that in women aged 20-89 the odds of breast cancer at a latitude south of 27 degrees was 2.1 to 2.4 times higher than at a latitude above 27 degrees.
Lead investigator, clinical dietician Kellie Bilinski, told AAP the link between latitude and breast cancer could be due to the reduced potential to synthesise vitamin D from sunlight at lower latitudes.
The decreased risk of skin cancer supported the theory, she said.
The results supported international suggestions that higher vitamin D concentrations were associated with the reduced risk of breast cancer, the paper's abstract said.
New Zealand Breast Cancer Foundation medical adviser Anna Bashford said this study was the first of its kind to show such marked differences between latitudes and breast cancer rates.
``There has been research looking at Vitamin D levels and that maybe low levels of Vitamin D are a risk factor for breast cancer, but the studies have been of mixed results.''
Dr Bashford said she was not aware of any similar research being undertaken in New Zealand.
``In New Zealand we're right up there with having a high rate of breast cancer per capita. There are other risk factors that have been thought in the past to account for that, such as high body weight, women leaving it later to have their first baby ... alcohol intake,'' she said.
``It's probably a complex puzzle and the Vitamin D is a small part in the jigsaw.''
It would be an interesting line of study to take in New Zealand, she said.
``I think it's a good start and there are lots of similarities between New Zealand and Australia, and they have a relatively high rate of breast cancer as well, but it will be interesting to replicate the same study here.''
The Australian investigators were now recruiting almost 600 Australian women who had been diagnosed with early breast cancer, to examine the relationship between their vitamin D levels and tumour growth.
New Zealand lies between 34 and 47 degrees latitude south - with the equator at 0 degrees and the South Pole at 90 degrees.