Terri Judd, The Independent — Health & Wellbeing, Monday, 19 May 2008
Women with a vitamin D deficiency when they are diagnosed with breast cancer have an increased risk of dying within 10 years, research has found.
Patients whose levels of the vitamin are below average are twice as likely to see the cancer spread, and 73 per cent more likely to die within a decade of diagnosis, according to a study due to be presented next month by the American Society of Clinical Oncology.
While the correlation between low levels of vitamin D and the increased risk of breast, prostate, pancreas, oesophagus and colon cancer is well documented, no previous attempt has been made until now to link it to patients' prognosis after the disease is discovered.
"This is the first study to look at the impact of vitamin D on outcomes of breast cancer," said the lead author, Dr Pamela Goodwin, an oncologist at Mount Sinai Hospital in New York and professor of medicine at the University of Toronto.
The researchers studied 512 women diagnosed with localised breast cancer between 1989 and 1995 and followed their progress for 10 years. At the time of diagnosis, 37.5 per cent had low levels of the vitamin, 38.5 per cent moderately low levels, and just 24 per cent had adequate levels.
Women who were pre-menopausal, weighed more, had high insulin levels or more aggressive tumours generally had a deficiency.
Among the women with adequate levels of the vitamin, 15 per cent died and 17 per cent experienced a spread in the cancer. But in those with low levels, 26 per cent died and 31 per cent suffered a cancer spread.
For some time vitamin D – produced when the body is exposed to sunshine and long considered important for healthy bone growth – has been feted as a key supplement, with evidence that it helps prevent or treat diabetes, multiple sclerosis, rheumatoid arthritis, muscle pain, depression, heart disease and stroke. However, there remains confusion about benefits and dosages.
"This study found that vitamin D deficiency is very common among women with breast cancer and suggests the deficiency is linked to poorer outcomes," said Dr Nancy Davidson, director of the breast cancer program at the Johns Hopkins Kimmel Cancer Center in Baltimore. However, Dr Goodwin warned: "It's premature to tell women with breast cancer they should take more vitamin D than is recommended for bone health. If you're a woman with breast cancer, it's worth having your vitamin D level checked. If you are deficient, take more to get it in the range we think is beneficial."
Dr Goodwin said the data suggested there may be a small increased risk of metastasis (spreading) or death if vitamin D levels are high, but not a statistically significant effect.