Dr. Oz recommends 1,000 IU daily. Health guru Dr. Andrew Weil recommends 2,000 IU. Now researchers have reported that an intake of 4,000 to 8,000 IU of vitamin D a day can prevent or markedly cut the incidence of breast cancer and several other major diseases. The findings from the University of California (UC) at San Diego School of Medicine and Creighton University School of Medicine in Omaha were published February 21 in the journal Anticancer Research.
“We found that daily intakes of vitamin D by adults in the range of 4,000-8,000 IU are needed to maintain blood levels of vitamin D metabolites in the range needed to reduce by about half the risk of several diseases—breast cancer, colon cancer, multiple sclerosis and type 1 diabetes,” said Cedric Garland, DrPH, professor of family and preventive medicine at UC San Diego Moores Cancer Center.

The study covered several thousand volunteers who were taking vitamin D supplements in doses ranging from 1,000 to 10,000 IU/day. Blood studies were conducted to determine the level of 25-vitamin D – the form in which almost all vitamin D circulates in the blood.

Numerous studies have shown a beneficial link between vitamin D and cancer prevention, as well as dementia, autoimmune disorders, metabolic syndrome and other conditions. One such study released in the October 2010 issue of Genome Research showed that vitamin D regulates 2,776 genes, including those involved in cancer and autoimmune diseases. In the study, 229 genes changed in response to vitamin D.

“It seems that if you are born with genes that increase your risk of [cancer and autoimmune] diseases, vitamin D may act to correct this genetic predisposition,” lead author Dr. Sreeram Ramagopalan of the Wellcome Trust Centre for Human Genetics at Oxford University told CNN.

Don’t run out and start popping vitamin D indiscriminately, though. The Institute of Medicine (IOM) is unconvinced. Last November, it released a report covering an exhaustive assessment of the current data on health outcomes associated with calcium and vitamin D. The IOM study concluded that there was clear evidence that vitamin D plays an important role in bone health but not in other health conditions. It found that information about the benefits of vitamin D beyond bone health “were from studies that provided often mixed and inconclu­sive results and could not be considered reliable.”  The study also found that average blood levels of vitamin D in the majority of the population meet what is needed for good bone health.

The committee of experts commissioned by the IOM did, however, raise the recommended daily allowance of vitamin D from 400 IU to 600 IU—not high enough, according to critics.

More is not always better

It is known that vitamin D levels above 10,000 IU per day can cause kidney and tissue damage. The IOM suggests 4,000 IU as the upper limit per day, stating that when “intakes of vitamin D surpass 4,000 IU per day, the risk for harm begins to increase.” However, in its report the IOM notes that the evidence for possible risk for harm at levels below 10,000 IU is limited.

Obviously, the debate goes on until more clinical trials can prove additional health benefits. In the meantime, to ensure you get some vitamin D, head out into the sunshine for five to 30 minutes twice a week. You should know, however, that sunscreen with an SPF of 8 or more blocks ultraviolet (UV) rays from producing vitamin D.

Commercial tanning beds that emit 2%–6% UVB radiation are also effective in providing vitamin D. But caution is needed. UV rays whether from the sun or tanning beds cause skin cancer—not to mention the wrinkles we’re all trying to avoid.

You can get vitamin D from some foods. It occurs naturally in egg yolks and fatty fish, such as salmon, tuna and mackerel. It is also added as a supplement to milk, as well as other dairy products, cereals and juice. Check the labels.

And if you decide to take vitamin D supplements, opt for vitamin D₃ vs D₂. Experts agree that D₃ is more potent, stable and lasts longer in the blood. Of course, before beginning to take any dietary supplement, talk to your doctor to discuss possible contraindications.