We spend most of our days in offices - modern glass doesn't allow the vitamin D-producing ultra violet B rays through - and for four to six months of the year the sun isn't high enough in the sky to stimulate production in the skin when you do go outdoors.

This is why Dr. Dowd recommends his patients take a supplement containing anywhere between 4,000 and 6,000 international units (IUs) a day. He says it is the only way to get their blood levels up to a point where the real benefits begin to kick in.

However vitamins don't work like a drug; you can't just take a three or four 1000 IU pills a day and assume that all will be well. Vitamin D works alongside three other minerals: potassium, magnesium and calcium, which are best obtained from your diet. Without these, vitamin D doesn't work as well.  Unfortunately, the typical American and British diets rarely have enough of these minerals either, says Dr Dowd.

Dr Dowd recommends a good intake of protein from lean meat along with nuts and seeds. While this protein also has an acidic effect, it has many other benefits and its acid count can be easily balanced by an increase in fruit and vegetables, he adds.

To prevent bonedamaging rickets you need an intake of about 400 IU a day. The UK Food Standards Agency cautions against supplementing with amounts over 1,000 IU because high levels have been linked with excess calcium which can damage bones and kidneys.

However, these safety levels are controversial. A recent article in the prestigious New English Journal of Medicine recommended that people take 2,600 IU per day.  Dr. Dowd himself says: "People worry about taking too much vitamin D but it is hard to overdose. Toxicity is highly unlikely with an intake of less than 10,000 IU a day."

A spokesperson for the British Nutritional Foundation pointed out that the safe upper limit for supplementing according to the American Institute of Medicine was 2,000 IU and warned of dangers of going above that."

The Vitamin D Cure, by James Dowd MD and Diane Stafford is published by John Wiley on January 23 at £13.99.

And from http://www.rd.com/the-miracle-vitamin/article28654-2.html comes the following:

Even after cancer strikes, the vitamin D our bodies make in the summer helps fight the disease. A study at Harvard found that mortality rates were 40 percent higher among lung cancer patients operated on in the winter than among those who had surgery in the summer and had high levels of D from sun or diet. This year, a British study found that survival rates there are highest among cancer patients diagnosed in the summer and fall. And last year in Norway researchers found higher survival rates among young people with Hodgkin's lymphoma diagnosed in the autumn.

Benefits aren't limited to D from the sun. In Canada, patients given vitamin D along with chemotherapy had fewer side effects and developed fewer thromboses (blood clots), serious complications of treatment, than those who got a placebo with chemo.

How can a mere vitamin harbor such amazing powers? For starters, D isn't really a vitamin. In the body, it is transformed into a benevolent hormone, shoring up our bones, regulating cell growth and helping prevent the kind of wild cell proliferation that leads to cancer. "Almost every tissue and cell in the body has receptors for vitamin D, which means that every tissue and cell needs vitamin D to function maximally," says Michael F. Holick, MD, a vitamin D researcher at Boston University.

In the lab, researchers have watched as activated vitamin D actually turns off cancer. When prostate cancer cells were exposed to D, the cells stopped reproducing wildly and resumed normal, orderly growth. Later studies showed that the same process occurs in colon and breast cancer cells. And when Dr. Holick's team gave vitamin D to mice with colon cancer, they witnessed a 40 percent reduction in tumor growth.

The big challenge now? Distilling the cancer-protective elements of vitamin D into compounds that can be used to treat humans.