Vitamin D & Colorectal Cancer

The new prescription for colon cancer prevention may soon include an afternoon in the sun followed by a tall glass of milk.  Several new studies in the past year have shown that by maintaining adequate serum Vitamin D levels, individuals may successfully prevent colon cancer as well as several other internal cancers.  Vitamin D is a fat soluble vitamin that is

found in some foods and can also be made by your body during exposure to ultraviolet UV light from the sun.  Since there are only a few commonly consumed foods that are good sources of vitamin D (see accompanying table), sunlight is perhaps the most important source of Vitamin D.  UV rays from the sun initiate vitamin D synthesis in the skin.  The extent of sunlight derived Vitamin D is impacted directly by factors that affect UV ray exposure including, season, geography, time of day, cloud cover, and sunscreen.  


Over two decades ago, researchers first recognized the importance of vitamin D from sunlight in preventing colorectal cancer.  They observed significantly higher mortality rates from colorectal cancer in the northern and northeastern United States, compared to the southwest, Hawaii and Florida, which correlated directly with an individual’s vitamin D status.  They showed that people who had higher levels of serum vitamin D, had lower rates of colon cancer.  Since then several observational and laboratory studies have investigated the association of serum vitamin D levels and colorectal cancer risk.  

Common Sources
of Vitamin D

Salmon
Fresh, wild (3.5 oz)  
600-1000 IU
Fresh, farmed (3.5 oz)
100-250 IU

Shiitake Mushroms
Fresh (3.5 oz)   
100 IU
Sun-dried (3.5 oz)
1600 IU

Sardines, canned (3.5 oz)
300-600 IU

Mackeral, canned (3.5 oz)
250 IU

Cod Liver Oil (1tsp)
400-900 IU
Tuna, Canned (3.6 oz)
230 IU
Egg yolk
20 IU
Fortified Milk (8 oz)
100 IU
Fortified Cheese (3.5 oz)
100 IU
Sunlight Exposure (5-10 minutes)
3000 IU
A new study using a sophisticated analytical technique known as a meta-analysis*, examined the data from five previous observational studies, each of which examined vitamin D and colorectal cancer risk with a  follow-up of 25 years.  The results of the meta-analysis revealed that by raising the serum level of vitamin D to 34 ng/ml, the incidence rates of colorectal cancer could be reduced by half.  Even higher levels of serum Vitamin D further reduced colorectal cancer risk, as head researcher Edward Gorham, Ph.D. reported,  “We project a two-thirds reduction in incidence with serum levels of 46 ng/ml, which corresponds to a daily intake of 2,000 IU of vitamin D3.  This would be best achieved with a combination of diet, supplements and 10 to 15 minutes per day in the sun.”  


Researchers in the Journal of the National Cancer Institute also reported on the protective effect of vitamin D in preventing colorectal cancer mortality.  After following the vitamin D status of 16,818 participants for 12 years, researchers determined that vitamin D exhibited a strong protective effect against colorectal cancer, with levels of 32 ng/ml or higher having a 72% risk reduction on colorectal cancer mortality.  In further support of Vitamin D, a recently completed epidemiological study of over 190,000 individuals, showed that both calcium and vitamin D from (from food and supplements) were protective against colorectal cancer.  Though researchers reported mixed results for men and women, “Total vitamin D intake was inversely associated with colorectal cancer risk in men but not in women.”   In yet another study from 2007, researchers in Japan suggest that a low level of plasma vitamin D may decrease the risk of rectal cancer, yet have little effect on colon cancer.  The researchers suggest that the reason for the distinction in its protective effect in the rectum but not the colon may derive from differences in the vitamin D receptor in these tissues. 

     
Vitamin D has certainly proven effective in colorectal cancer prevention, though the question of how much vitamin D to take is still in dispute.    In 1997 the Food and Nutrition Board of the Institute of Medicine recommended that healthy individuals who are not exposed to sunlight should adequately consume vitamin D from dietary sources in the following amounts:


       Ages 19-50:  200 IU       Ages 51-69:  400 IU        Age 70 and older: 600 IU

 
Many experts today believe these recommendations are far too low, citing that even brief exposure to sunlight can produce up to 3000 IU of vitamin D, which is considered a tolerable and therapeutic dose.   They recommend that healthy adults regulate vitamin D intake to 1000-2000 IU daily, which represents the tolerable upper intake levels set by the Institute of Medicine.   There is a high health risk associated with consuming too much vitamin D, as vitamin D toxicity can cause nausea, constipation, weakness, weight loss and neurological problems.   Consuming too much vitamin D from dietary sources and sunlight is virtually unheard of, though caution should be taken with any supplemental sources of Vitamin D.  Caution should also be taken not to overdo exposure to sunlight, as excessive UV radiation from the sun damages skin cells and may cause certain types of skin cancer.

                          *What is a Meta-Analysis?   

A meta-analysis combines the data and results of several related studies.  By performing a meta-analysis researchers are able to increase the statistical power, precision and the overall significance of the findings, since random fluctuation in any one study may be counterbalanced by results of other studies.