An Introduction to Cancer Patient friendly summary

 "No other method to prevent cancer has been identified that has such a powerful impact."

~ Dr. Cedric F. Garland, vitamin D expert and Professor, Department of Family and Preventive Medicine Cancer Prevention and Control Program, Moores Cancer Center at University of California, San Diego

What is cancer?

Cancer is the uncontrolled growth of abnormal cells that can occur anywhere in the body when damaged cells fail to undergo apoptosis, or programmed cell death. Oftentimes, cancer begins in one area of the body and then spreads to one or more other areas, a process known as metastasis.

A leading cause of death world-wide, the number of deaths due to cancer are expected to increase to an estimated 12 million by the year 2030.

Risk factors

The most commonly-recognized risk factors for cancer are:

  • Environmental toxins
  • Smoking
  • Alcohol consumption
  • Obesity
  • Lack of exercise

But there are other known, less-recognized, risk factors.

High intake of meat and dairy

Eating a diet high in animal products early in life causes the body to produce more insulin-like growth factor (IGF). IGF helps the body grow, but it also helps tumors grow. Many cancers that are prevalent in the United States and Europe are uncommon in developing countries that do not have high amounts of animal products in their diet. Such countries who have Westernized their diets have had dramatic increases in their cancer rates.

Sunlight exposure and cancer risk

 Sunlight has a direct effect on reducing most cancer risks.

Sunlight has a direct effect on reducing risk of many types of cancer. The shortwave ultraviolet portion of sunlight, ultraviolet-B (UVB), stimulates the body to produce vitamin D, which protects against cancer.

Solar ultraviolet light is also a risk factor for skin cancer and melanoma. The risk of skin cancer is highest for people with pale skin, who have sunburned a number of times, or who spend a lot of time in the sun for work or other reasons. Those who work in the sun generally do not have an increased risk of melanoma.

The number of cancer cases and deaths vary with the amount of regional sunlight for many types of cancer. According to cancer studies, there are:

  • Lower rates in the sunny Southwest United States and higher rates in the darker Northeast
  • Higher rates in countries that are farther from the equator and receive less sunlight

Vitamin D and cancer

Vitamin D reduces the risk of many types of cancer. The evidence comes from the following numerous types of studies:

  • Ecological studies define populations geographically such as by state or country generally find lower cancer incidence or mortality rates in regions that have more solar UVB or are closer to the equator.
  • Observational studies compare people with cancer to those without the disease. Studies that use short intervals between vitamin D intake or blood levels and cancer incidence are more likely to find the effect of vitamin D on cancer risk since vitamin D levels MAY change with time.
  • One randomized controlled trial of vitamin D supplementation confirmed the benefits in reducing risk of cancer for those taking vitamin D compared to those not taking vitamin D.
  • In addition, numerous laboratory studies have been done to investigate the mechanisms of vitamin D in reducing risk of cancer incidence, growth, and spread.

The evidence of vitamin D benefits is strongest for colon, rectal, and breast cancer. Vitamin D also protects against cancer of the bladder, brain, endometrial lining, esophagus, gallbladder, kidney, lungs, ovaries, pancreas, prostate, and stomach. In addition, vitamin D protects against Hodgkin’s and non-Hodgkin’s lymphoma, leukemia, multiple myeloma, and melanoma.

Vitamin D levels

 Vitamin D levels greater than 40 ng/mL (100 nmol/L) reduce the risk of cancer.

The rates of breast, colon, and rectal cancer decrease rapidly as vitamin D levels increase from very low levels [less than 10 ng/ml (25 nmol/] out to 20-30 ng/ml, then decreases at a slower rate until levels reach about 50 ng/ml (125 nmol/l). No comparable findings have been reported for other types of cancer. However, it is assumed that they behave in a similar manner since incidence and mortality rates are similar in geographical studies.

How vitamin D works

Vitamin D has been shown to block the growth of cancer tumors. Calcitriol, an active form of vitamin D, is produced by the body by various organs after vitamin D is processed processed by the liver. Calcitriol provides numerous benefits against cancer. This form of vitamin D encourages cells to either adapt to their organ or commit apoptosis. Calcitriol also limits blood supply to the tumor and reduces the spread of cancer.  


High levels of vitamin D are associated with a lower risk of many types of cancer in both observational studies on individuals and geographic studies of populations.

Vitamin D

Based on studies of breast, colon, and rectal cancer, vitamin D levels of 40–60 ng/mL (100–150 nmol/L) reduce the risk of cancer. Taking 1000–4000 international units (IU) (25–100 mcg)/day of vitamin D is associated with reduced breast cancer risk.

Vitamin D and calcium

Studies have shown that taking both vitamin D and calcium provides additional cancer protection for many types of cancer. Calcium intake of more than 1000 mg/day from either diet or supplements is recommended.

Patients in one study took daily doses of 1100 IU (27.5 mcg) vitamin D and 1450 mg calcium. These patients had a 77% reduction in the incidence of all types of cancer between the ends of the first and fourth years of the study compared to those taking a placebo.


People with higher vitamin D levels at time of cancer diagnosis often have a higher survival rate. This has been verified for people with breast, colorectal, lung, and prostate cancer; non-Hodgkin’s lymphoma; and melanoma. These studies suggest that increasing vitamin D levels after cancer diagnosis may improve chances of survival.

Some cancer treatment centers are now giving at least 5000 IU (125 mcg)/day vitamin D to patients with cancer. Outcome results have yet to be published.

Find out more...

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on An Introduction to Cancer.

Page last edited: 01 September 2011