Questions and Answers About Vitamin D
- What is vitamin D?
Vitamin D has many actions in the body including:
Vitamin D is needed for bone growth and protects against osteoporosis in adults. Vitamin D level is usually checked by measuring the amount of 25-hydroxyvitamin D in the blood.
- What are the sources of vitamin D?
- Have any preclinical (laboratory or animal) studies been conducted using vitamin D?
Preclinical studies of vitamin D in prostate cancer have shown the following:
- A study of a form of vitamin D showed that it may prevent prostate cancer cells from sticking to endothelium, the thin layer of cells that lines the inside of blood vessels, lymph vessels, and body cavities.
- In a 2011 study, mice were fed a diet with adequate vitamin D or a diet lacking vitamin D and were then injected with prostate cancer cells into bone marrow or into soft tissues. The mice lacking vitamin D developed bone tumors that were larger and grew faster than the mice that had adequate levels of vitamin D. However, there was no difference in soft tissue tumors among mice with different vitamin D levels. Results of this study show that a lack of vitamin D is linked with growth of prostate cancer cells in bone but not in soft tissue.
- A study of vitamin D as adjuvant therapy (therapy to make other types of treatment more effective) combined it with cryotherapy (freezing). Mice injected with prostate cancer cells were treated with calcitriol with or without cryotherapy. Those who were treated with the combination of calcitriol and freezing had more cancer cell death and less cancer cell spread than those who were treated with either calcitriol alone or freezing alone.
- Have any population studies or clinical trials (research studies with people) of vitamin D been conducted?
Population studies look for risk factors and ways to control disease in large groups of people. Population studies of vitamin D and prostate cancer risk have shown the following mixed results:
- Vitamin D levels in patients with prostate cancer that had not spread were taken annually for 5 years. Throughout the course of the study, lack of vitamin D was a common finding among these patients.
- Another study in patients with prostate cancer suggested that medium or high levels of vitamin D in the blood may be linked with better outcomes than lower levels. These findings indicate that vitamin D levels may play a role in whether or not the disease will worsen and may be a factor in predicting outcome in prostate cancer patients.
- One thousand patients with prostate cancer and 1000 control patients in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study were followed for up to 20 years. Results suggested that men with higher blood levels of vitamin D had a greater risk of developing prostate cancer than men with lower vitamin D levels.
- In a case-cohort analysis from the Selenium and Vitamin E Cancer Prevention Trial (SELECT), men who had moderate blood levels of vitamin D (45–70 nmol/L) were found to have a markedly lower risk of aggressive prostate cancer than men who had either lower or higher levels of vitamin D.
- Vitamin D from sunlight exposure has been studied for possible effects on prostate cancer rates. A 2006 study found that PSA levels rise at a slower rate during the spring and summer compared to other times of the year, suggesting this may be due to higher vitamin D levels during those months. Another study found that while men with low levels of sun exposure had increased risk of all prostate cancers, those with prostate cancer who had less sun exposure showed lower risk of advanced disease.
- Geographic patterns of deaths in the United States from 1950 to 1994 showed that higher death rates from prostate cancer occurred in parts of the country with lower levels of UV radiation from sunlight. This effect is strongest in places more than 40 degrees north of the equator, where sunlight is weakest during the winter months. These findings support the theory that lack of vitamin D increases the risk for prostate cancer.
Reviews of many population studies combined
A 2008 review of 45 observational studies combined found no link between intake of vitamin D and prostate cancer risk.
A 2011 review of 25 studies combined found no link between either vitamin D in the diet or blood levels of vitamin D and the risk of prostate cancer.
A 2014 review of 21 studies combined found that high levels of vitamin D in the blood may be linked with a higher risk of prostate cancer. Many factors may affect these findings, since some studies propose men from higher income groups may have higher vitamin D levels and are more likely to get PSA testing, leading to higher rates of reported prostate cancer.
Clinical trials of treating prostate cancer
Clinical trials in patients with prostate cancer have shown the following:
- A clinical trial treated patients with prostate cancer that had recurred (come back) with calcitriol (the active form of vitamin D) and naproxen for 1 year. Results showed that the combination of calcitriol and naproxen was effective in slowing the rate of rising PSA levels in study patients, suggesting it may slow disease progression.
- In a 2010 study, patients with prostate cancer that did not respond to hormone therapy were treated with calcitriol and dexamethasone. The results indicated that while the treatment was well tolerated, it did not have an effect on PSA levels in the study patients.
- In a 2009 study, patients with locally advanced or metastatic prostate cancer were treated with vitamin D. The study reported that one in every 5 patients who took vitamin D had improved PSA levels, suggesting that vitamin D may be an effective therapy for patients with advanced prostate cancer.
- Is vitamin D approved by the U.S. Food and Drug Administration (FDA) for use as a cancer treatment in the United States?
Vitamin D is available in the United States in food products and dietary supplements. Because dietary supplements are regulated as foods, not as drugs, FDA approval is not required unless specific claims about disease prevention or treatment are made.
Current Clinical Trials
General information about clinical trials is also available from the NCI Web site.