A daily dose of 'sunshine' vitamin D could slash cancer deaths by 12 per cent according to a new study.
Vitamin D deficiency is widespread and is particularly prevalent in cancer patients.
The vitamin is made by the body when exposed to sunlight but is also found in oily fish such a salmon as well as red meat, liver and egg yolks.
Around 15 per cent of Germans in the study were deficient in the vitamin over a year but amongst colorectal cancer patients this shot up to 59 per cent and was associated with a bad prognosis.
Researchers from the German Cancer Research Center looked at 14 different studies involving 105,000 people.
Dr Ben Schöttker, an epidemiologist at the Center said: "Based on current studies, vitamin D3 supplementation probably does not protect against developing cancer but it could reduce the likelihood of dying from cancer.
"However, previous studies on cancer mortality have yielded very different results, and we were interested in the reasons for this.
"By re-evaluating all previous studies on the topic, we wanted to help produce robust results on this issue, which is so relevant to population health."
To investigate the effectiveness of vitamin D3 on cancer mortality in the population and on the survival of cancer patients the researchers considered only studies of the highest quality whose participants had been randomly assigned to the vitamin D3 arm or the placebo arm.
They found that a daily low dose of vitamin D at 400 to 4000 IU (international units) per day was more effective than a larger dose of 60,000 to 120,000 IU once per month or less.
Dr Schöttker said: "In the four studies with the infrequent higher doses, there was no effect on cancer mortality.
"In contrast, in the summary of the ten studies with daily dosing, the researchers determined a statistically significant 12 per cent reduction in cancer mortality."
"We observed this 12 per cent reduction in cancer mortality after untargeted vitamin D3 administration to individuals with and without vitamin D deficiency.
"We can therefore assume that the effect is significantly higher for those people who are actually vitamin D deficient."
A more detailed analysis of the studies with daily intake further revealed that people aged 70 and older benefited most from vitamin D3 therapy.
In addition, the effect was most evident when vitamin D intake was started before the cancer diagnosis, according to the study published in the journal Ageing Research Reviews.
Dr Schöttker thinks the low regular doses are better because the vitamin reacts with the body to produce a hormone that inhibits cancer growth.
Professor Hermann Brenner, epidemiologist at the Center added: "This work underlines the great potential of vitamin D3 administration in the prevention of cancer deaths.
"Regular intake at low doses is associated with almost negligible risk and very low cost."
The current work was supported by German Cancer Aid.
