The prospective study, published in the journal Cancer Causes and Control, analysed data from 1,200 healthy women, finding that those with low levels of the sunshine vitamin in the three months before a cancer diagnosis is confirmed are around three times more likely to developing breast cancer than those women with the highest vitamin D levels.
The team, led by Professor Cedric Garland from UC San Diego, USA, examined whether a relationship exists between pre-diagnostic serum levels of 25-hydroxyvitamin D (25(OH)D) and risk of breast cancer in young women by examining the relationship in 600 breast cancer patients and 600 matched controls.
Garland says the study findings point to the possibility of a relevant window of time for cancer prevention in the last three months preceding tumour diagnosis – a time that he notes is physiologically critical to the growth of the tumour.
"While the mechanisms by which vitamin D could prevent breast cancer are not fully understood, this study suggests that the association with low vitamin D in the blood is strongest late in the development of the cancer," said Garland.
Garland and his team picked the 1,200 case controlled samples from 9 million blood serum specimens from young women frozen by the US Department of Defense Serum Repository for routine disease surveillance.
They thawed and analysed pre-diagnostic samples of serum from 1,200 women whose blood was drawn in the same time frame – samples from 600 women who later developed breast cancer, and from 600 women who remained healthy.
The researchers found that women whose serum vitamin D level was low during the three-month period just before diagnosis had approximately three times the risk of breast cancer as women in the highest vitamin D group.
According to Garland, this is likely to be the point at which the tumour may be most actively recruiting blood vessels required for tumour growth.
"Based on these data, further investigation of the role of vitamin D in reducing incidence of premenopausal breast cancer, particularly during the late phases of its development, is warranted," he said.