There is a strong link between UV exposure and death rates from many cancers — especially those in the stomach and intestines. Most at risk are men, in whom about 80% of these cancers were due to low sun exposure. In women, UV rays were linked to cancers in gastrointestinal and reproductive organs. Over in Japan, they found more proof that low sun exposure was linked to death rates from cancers such as those affecting the esophagus, stomach, colon, rectum, pancreas and gallbladder, and bile ducts.
In a five-year study with more than 120,000 people, men with the highest intake of vitamin D had a 29% lower risk of colorectal cancer (compared to those with the lowest vitamin levels. (It was not, though, linked to cancer risk in women.) In a recent review, Harvard researchers said that a dosage of 200-400 IU/day of vitamin D may be too low for cancer-fighting benefits. In other words, the sun is most important.
Another study found that getting 1,000 IU of D supplements could reduce your risk of colorectal cancer by 50%. Plus, 1,200 mg a day of calcium supplements lowered the risk of all colon polyps. Using both nutrients together is the best way to prevent cancerous developments in the colon.
Not all studies say this, mind you. A few in 2005 and 2006 found that women don’t seem to reap the cancer preventative benefits. There may have been problems with some of these studies, such as not following the patients for long enough.