Studies indicate Vitamin D and calcium may affect colon cancer
Epidemiologists from UC San Diego recently revealed that Vitamin D and the mineral calcium may have more to do with cancer of the colon than does fiber or any other elements. And eating foods rich in calcium and Vitamin D may be the best step to prevent colorectal cancer, the second most deadly cancer in the United States.
Speaking to food writers at a recent nutrition news conference here, Cedric Garland, assistant professor of epidemiology at the School of Medicine, UC San Diego, said that clues to the effects of calcium and Vitamin D in the diet were traced to epidemiological surveys showing that death rates from colon cancer in the United States are highest in populations least exposed to natural light.
The most sunlight in the United States is found in southern California, Arizona and New Mexico, where, according to Garland, rates of colon cancer are the lowest overall. The mortality rate from colon cancer in the northern half of the country is double that of the southern half. New Hampshire has nearly three times the mortality rate for colorectal cancer as the southern states. “Sunlight actually striking the Earth is a better predictor of the colon cancer rate than is latitude. And we all know that sunlight creates Vitamin D in people,” Garland said.
Similar epidemiological investigation of the worldwide picture based on the link between sunlight and colon cancer revealed that the lowest rates of colon cancer in the world occurred in the Dominican Republic, the Philippines, Honduras, Costa Rica and Martinique, which are close to the equator. The farther away from the equator, the higher the risk of colon cancer. “People from Scotland or the Scandinavian countries were at very high risk,” Garland said.
Japan the Exception
Only Japan, which is in the same latitude as San Francisco, confused the theory. Japan has less than a third of the colon cancer death rate as does San Francisco, where risk is high relative to Southern California cities.
Garland explained the discrepancy: “Japan is a maritime country and the people have always eaten Vitamin D-rich fish. Even today, most of the protein in the Japanese diet comes from fish--many more times than the proportion of our protein that comes from fish. This aspect of the Japanese diet was a clue that suggested to us that the common link in living in near-equatorial regions and being Japanese was Vitamin D.”
In 1980, in the International Journal of Epidemiology, the epidemiologists revealed their theory that Vitamin D from the sun was preventing colon cancer in much of the world. “We also proposed that Vitamin D from the diet was helping to prevent it where the diet contained a reasonable amount of Vitamin D.
“Vitamin D, we theorized, was acting in its role as a hormone to cause absorption of calcium. The calcium, we proposed, was reducing the rate of turnover of the cells lining the colon,” Garland said. “And this, in turn, was reducing the vulnerability of those cells to cancer-causing agents because the cells that are turning over are the ones that can be attacked by the cancer causers. Cells that are in a quiescent state, that are not turning over, are very resistant to carcinogens. In the absence of Vitamin D and the absence of calcium, the cells start to turn over extremely quickly. When they do that, any carcinogen that happens to be nearby can tear them apart and induce a cancer.”
The scientists theorized that the more intense exposure to sunlight and subsequent increased production of Vitamin D in the body was the key to the lower risk for colon cancer.
It was on this basis that the scientists suggested that exposure to sunlight might help reduce the risk of colon cancer by increasing the levels of Vitamin D, calcium-binding protein and biologically active calcium.
These ecological findings led to the study in which Garland and his team investigated whether dietary Vitamin D and calcium were associated by following up a previous study which had been conducted in 1957 and 1958 by Dr. Richard Schedkele at the University of Chicago and Harvard University, detailing food histories of 1,954 workers at a Western Electric Plant near Chicago.
In 1977, a followup was made to determine the health status of the men in the study. Of those men, 49 had developed colorectal cancer.
The 1,954 men were divided into four groups on the basis of outcome after 19 years of diet history. The men with colorectal cancer formed one group, men with other malignancies another, men who died but had no cancer diagnosed formed the third group and men who were alive and free of known cancer at the end of the 19 years formed the fourth group.
Other Factors Ruled Out
The results of the study supported the suggestion that Vitamin D and calcium may reduce the risk of colorectal cancer. Other dietary factors were ruled out.
“We looked at almost everything: saturated, unsaturated and polyunsaturated fat intake, vegetable protein, cigarettes, body weight, age and alcohol consumption. Men who did and didn’t have the cancer were surprisingly similar in their life styles. The only differences were in Vitamin D and calcium intakes,” Garland said.
The differences in the intake of animal protein between the non-cancer and the cancer groups were slight, and not significant. The differences in the intake of vegetable protein were also slight, and not significant. Both groups shared the typical North American high-fat diet, about 42% to 43% fat. The investigators also analyzed the fats by type--polyunsaturated, unsaturated and mono-unsaturated fats--and found no difference of note.
There also were no differences in the intake of dietary cholesterol between the groups, nor was there a significant difference in carbohydrate intake. There was also no significant difference in intake of any type of alcoholic beverage, or intake of phosphorus, iron, Vitamin C, thiamine, riboflavin and niacin. Only Vitamin D and calcium were significantly related to the risk of colon cancer. “The more Vitamin D and calcium, the less colon cancer there appeared to be,” Garland said.
The men were then divided into four groups of about 500 men each, according to dietary intake of Vitamin D. The men in the two groups highest in Vitamin D had the lowest incidence rates of colon cancer. The scientists found that the threshold effect of Vitamin D intake is at about 155 International Units of Vitamin D per day. “Beyond that, it doesn’t appear that there is any additional benefit. Less than that and you are in trouble. But we don’t know why this is so,” Garland said.
The test was repeated for calcium intake. “And here the relationship was smoother, with no evidence of a threshold. Men who consumed the least calcium had the highest rate of colorectal cancer. Those who consumed the most calcium had the lowest rate,” Garland said.
Garland, however, does not consider the evidence definitive. “It’s possible that dietary intake of calcium and Vitamin D might be a marker for dietary intake of something else which we did not identify, but which protects against colon cancer. It’s possible that people who took in very little Vitamin D and calcium might have a defect, causing them to be intolerant of the sources of Vitamin D and calcium and that the defect might be the cause of the cancer.
“It’s also possible that the intake of calcium and Vitamin D is a marker for cultural or other dietary practice which is important in the etiology of colon cancer, but not related to calcium and Vitamin D directly. These are all questions that we can’t answer and more studies are needed before the results can be considered definitive,” he said.
Garland cautioned against the intake of Vitamin D-containing pills because of the possibility of overdose or lack of therapeutic benefit. “Our study was based on dietary intake of foods containing Vitamin D or calcium such as milk and milk products, fish and certain vegetables. Any recommendation based on it should be restricted to the nutrients in these and other foods, or to the effects of sunlight,” Garland cautioned.
He also warned against the risk of skin cancer in the case of sunlight exposure and the risk of recurrence of kidney stones in people who have a history of them. “If our findings are replicated elsewhere, increases in the dietary intake of calcium and Vitamin D by Americans should be considered for the general population at all ages.
“We have probably not figured out the whole truth in this developing epidemiological mystery, but as Sherlock Holmes said to a trusted friend as the two lit out on a new adventure, ‘Come, Watson, come, the game is afoot.’ ”
