Compared to women who stay indoors, women with more exposure to sunlight have only half the chance of developing advanced breast cancer, which is cancer that has spread beyond the breast.

But this seems to happen for women with naturally light skin only.

According to researchers from the University of Southern California and Wake Forest University, the vitamin D that we get from sunshine may be important in slowing down the spread of breast cancer cells.

The scientists believe this effect was not seen in women with naturally darker skin because the sun produces up to 10 times more vitamin D in light-skinned women.

These results are consistent with an earlier study showing that women with regular sun exposure have less chance of developing breast cancer as compared to women who stay indoors.

The researchers caution women to avoid sunbathing, though, because of the risks of skin cancer.

But there are other ways to get vitamin D: supplements, fatty fish, or fortified foods such as milk, some cereals and fruit juices.

More studies need to be done.

But if they are consistent with this study, then an increase in vitamin D from diet and supplements may be a safer way to reduce breast cancer risk than too much sun exposure.