A study of more than 700 women found those boosting their diets with nutrients were up to 40 per cent less likely to develop the disease.
Lead researcher Professor Jaime Matta said: "It is not an immediate effect. You don't take a vitamin today and your
breast cancer risk is reduced tomorrow.
"However, we did see a long-term effect in terms of breast cancer reduction."
Prof Matta, of the Ponce School of Medicine in Puerto Rico, said calcium helps repair cells' DNA repair, a complex biological process involving more than 200 proteins that, if disrupted, can trigger tumours.
He said: "This process involves at least five separate pathways and is critical for maintaining genomic stability.
"When the DNA is not repaired, it leads to mutation that leads to cancer."
His team analysed 268 women with breast cancer and 457 healthy controls and found vitamin supplements reduced the risk of breast cancer by about 30 per cent.
Calcium supplements were even more successful, lowering incidence by 40 per cent.
They also showed women were more likely to have breast cancer if they were older, had a family history of breast cancer, had no history of breastfeeding and had lower DNA repair capacity.
Prof Matta, who presented his findings at a meeting of the American Association for Cancer Research in Washington DC, added: "We're not talking about mega doses of these vitamins and calcium supplements, so this is definitely one way to reduce risk."
Previous research has also suggested foods rich in calcium and vitamin D – including oily fish and green vegetables – can protect younger women against breast cancer up until they undergo the menopause. In the US, milk is included in this list, but in the UK it is not fortified and has negligible vitamin D,
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