Bowel cancer patients with high levels of vitamin D in their blood are more likely to survive the disease, a study shows. Patients with the highest levels of vitamin D have half the risk of dying compared with those with the lowest levels, the findings reveal. The study is the first to correlate total blood levels of vitamin D in bowel cancer patients after their diagnosis — which includes that produced after exposure to sunlight and that obtained from dietary sources — with their long term survival prospects.