How does this work? There is in fact a scientific answer. The sun stimulates production of a hormone in your skin. Ultraviolet B rays, the kind of rays that give you sunburns, interact with a special cholesterol in unblocked skin. Once stimulated, this cholesterol triggers your liver and kidney to make vitamin D3. Vitamin D3 isn't exactly a vitamin, but rather a type of steroid hormone that can drastically improve your immune system function.

Vitamin D3 also controls cellular growth and helps you absorb calcium from your digestive tract. Most importantly, this hormone/vitamin inhibits the growth of cancer cells. In laboratory tests performed on animals, vitamin D3 inhibited the growth of malignant melanoma, breast cancer, leukemia and mammary tumors. Vitamin D3 also slowed down angiogenesis, which aids the growth of cancer cells. Vitamin D3 stops cancer-aiding blood vessels from being formed, curbing the tumor's ability to spread and disrupt other functions in the body. Donald R. Yance Jr. writes that vitamin D3 may also inhibit the activity of hormones such as estrogen in breast cancer, thereby decreasing its spread.

Since high doses of vitamin D3 are toxic, scientists have formulated vitamin D derivatives that can be administered to breast cancer patients. In tests, these derivatives have stopped the proliferation of breast cancer cells and sometimes have actually decreased the size of experimental mammary tumors. Further findings like these might point to yet another undiscovered function of vitamin D3: regulating the expression of protein products that prevent and even inhibit breast cancer.

There is a concern relevant to this issue. Haven't we been told for the last 10 years to stay out of the sun? What about skin cancer? Dr. Richard Hobday, author of The Healing Sun, says our fear of the sun does more harm than good. Most recommended daily sunscreens block ultraviolet B rays, the same rays that trigger the production of vitamin D. The number of people who die from breast cancer, colon cancer, prostate cancer, ovarian cancer, heart disease, multiple sclerosis and osteoporosis -- all maladies that sunlight could benefit -- is far greater than the number of deaths from skin cancer. After reviewing 50 years of medical literature on cancer, Dr. Gordon Ainsleigh concluded that the benefits of regular sun exposure outweigh the risks of squamous-basal skin cancer, accelerated ageing and melanoma.

Despite the obvious advantages, most Americans are not getting enough vitamin D. Massachusetts General Hospital recently found that 59 percent of hospitalized patients had too little vitamin D in their bloodstream. Many experts infer that the Massachusetts vitamin D deficiency is almost as widespread in the general American population. Evidence also suggests that people with heavily pigmented skin (darker skin color) require more sunlight for adequate vitamin D production.

Given the obvious need for vitamin D, many researchers are looking for other sources for providing it to patients. While sunlight is the best naturally occurring source of vitamin D3 for humans, there are alternatives to a leisurely walk in the sun. Sheldon Saul Hendler, MD, PhD, describes an interesting paradox: While people living in Japan are exposed to relatively low levels of sunlight, the incidence of cancer among Japanese is very low. Hendler claims that the resistance to cancer apparent among the Japanese is explained by their diet, which includes large quantities of fatty fish that are rich in vitamin D.

Other sources of vitamin D include salmon, tuna, fish oils and vitamin D supplements. If you plan on drinking vitamin D fortified milk, however, be warned: Researchers at Boston University School of Medicine found the labels misleading. 80 percent of milk samples contained either 20 percent less or 20 percent more vitamin D than the amount advertised on labels. Too much vitamin D can be toxic and cause calcification in the kidneys and heart. So watch for the warning signs: anorexia, disorientation, dehydration, fatigue, weight loss, weakness and vomiting.

The Experts Speak On Sunlight and Breast Cancer

In tropical nations, where exposure to sunlight is normal, the incidence of osteoporosis, hip and spinal fracture, cataracts, and colon and breast cancer is less common. The lack of sunlight seen in cold climates in winter causes a failure of adequate vitamin D production which damages the immune system and may lead to more cancer than is seen in warm climates where vitamin D levels tend to be higher.
A Physicians Guide To Natural Health Products That Work By James Howenstine MD, page 173

Cancer: A ten-year epidemiological study conducted at Johns Hopkins University Medical School, in Baltimore, Maryland, showed that exposure to full-spectrum light (including the ultraviolet frequency) is positively related to the prevention of breast, colon, and rectal cancers. Another report found that exposure to full-spectrum sunlight reduced the risk of developing breast cancer. In Russia, a full-spectrum lighting system was installed in factories where colds and sore throats had become commonplace among workers. This lowered the bacterial contamination of the air by 40%-70%. Workers who did not receive the full-spectrum light were absent twice as many days as those who did.
Alternative Medicine by Burton Goldberg, page 305

Sunlight stimulates a hormone in skin that triggers the liver and kidney to make the active form of vitamin D3. Two equally effective sources of vitamin D in humans are derived from plant ergosterol, which is converted to ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) by the action of sunlight on the skin. The body uses vitamin D3 for normal immune system function, to control cellular growth, and to absorb calcium from the digestive tract. Vitamin D3 can inhibit the growth of malignant melanoma, breast cancer, leukemia, and mammary tumors in laboratory animals. Vitamin D3 can also inhibit angiogenesis, the growth of new blood vessels that permit the spread of cancer cells through the body. In warm weather, about 10-15 minutes of direct sun (in morning or late afternoon, to avoid skin damage) two to three times a week can produce sufficient vitamin D. As we age, however, our skin becomes less efficient at making vitamin D. People who live in cloudy climates with long winters may not get enough vitamin D. Many health experts believe that adults may benefit from 400 to 800 international units of vitamin D. But don't exceed this amount without your doctor's advice, since too much vitamin D can be toxic. Vitamin D can cause calcification in the kidneys, heart, and other tissues. Symptoms of vitamin D toxicity include anorexia, disorientation, dehydration, fatigue, weight loss, weakness, and vomiting.
Permanent Remissions by Robert Haas MS, page 215

Vitamin D may have the ability to inhibit the proliferative activity of hormones, such as estrogen in breast cancer, and has been shown to suppress breast and prostate cancer growth. Sunlight exposure, which leads to an increased level of vitamin D, correlates with a reduced risk of breast cancer. I usually recommend small amounts of vitamin D (400 to 1,000 IU) for those people without sunlight exposure, especially during the winter. I also occasionally recommend cod liver oil during the winter months as a source of vitamin D and omega-3 fatty acids. Vitamin D deficiency is very common in the elderly and in people who live in parts of the world with little sunlight; it is also one of the major contributing factors to osteoporosis.
Herbal Medicine Healing Cancer by Donald R Yance Jr, page 186

Vitamin D3 can be toxic in doses required to slow down the spread of breast cancer, so scientists have formulated vitamin-D derivatives that inhibit the proliferation of breast cancer cells and cause regression of experimental mammary tumors. Taken together, these facts suggest that vitamin D and its derivatives may play a role in regulating the expression of genes and protein products that prevent and inhibit breast cancer. The cancer-stopping power of vitamin D has been documented in osteosarcoma (bone cancer), melanoma, colon cancer, and breast cancer. These cancer cells contain vitamin-D receptors that make them susceptible to the anticancer effects of this vitamin-hormone made by the skin when it is exposed to sunlight. Vitamin D-rich foods include salmon, tuna, fish oils, and vitamin D-fortified milk and breakfast cereals. Caution: Since vitamin D can be toxic in high doses.
Permanent Remissions by Robert Haas MS, page 108

A study comparing the health habits of 133 breast cancer patients with women who did not have the disease found that exposure to sunlight lowered the risk of breast cancer by 30 to 40% or more. In reaction to sunlight exposure, the body manufactures vitamin D, which is thought to confer the protective effect.
Reducing Cancer Risk by Richard Harkness Pharm FASCP, page 98

Women who live in southern states are known to get breast cancer significantly less than those who live in the North. Some northern states don't get enough sun from November to February to make the required levels of vitamin D. "It's possible that all it takes is 10 or 15 minutes outside in bright sunlight to get a benefit," said Esther John, an epidemiologist at the Northern California Cancer Center. "And that's just casual exposure. The sunlight you get on your face and neck and arms and hands when you're regularly dressed." So while the exact dose of sunlight needed is not known, a brief outdoor stroll might do it. She said the amount needed to protect against breast cancer is probably not enough to cause skin damage. Sunscreens that block ultraviolet rays would also block the formation of vitamin D. However, we don't really know for sure if the benefits of sunlight are actually due to vitamin D. Other unrecognized factors may be involved.
Reducing Cancer Risk by Richard Harkness Pharm FASCP, page 98

However, there is mounting evidence that vitamin D from sunlight and fish oil may reduce the incidence of certain cancers, such as breast cancer. Hence, some vitamin D residuals in the fish oil may actually increase its protective value against cancer as well as CHD.
Textbook of Natural Medicine Volumes 1-2 by Joseph E Pizzorno and Michael T Murray, page 735

Numerous research papers have shown that metabolites (breakdown products or derivatives) of active vitamin D can actually suppress the growth and spread of malignant melanoma cells. Your eyes aren't playing tricks on you. We indeed just said that active vitamin D can retard the development and spread of melanoma. It is a tumor-inhibiting hormone. And what's more, its effects reach much farther than the skin; research has shown that active vitamin D can also impede the growth and development of breast cancer, colon cancer, and cancer of the prostate. And where do we get active vitamin D? From the sun—from the interaction of the UVB portion of sunlight with the special cholesterol in our unblocked skin. If adequate sunshine and vitamin D production can impede the development of these malignancies, then it stands to reason that inadequate amounts may promote them. And indeed that appears to be the case. Some researchers have even speculated that the inadequate vitamin D production that occurs in people with heavily pigmented skin living in geographic locations with limited sunlight, such as in northern latitudes and in the winter, might in part explain why these cancers behave so much more aggressively in black Americans (who, because of heavier pigment, may require more sunlight for adequate vitamin D production) than in white ones. (The same might be true for the millions of people who would never dream of going outside without covering every exposed inch of skin with a strong sunblock to "protect them.")
The Protein Power Lifeplan by Michael R Eades MD and Mary Dan Eades MD, page 242

Breast cancer rates vary directly with the amount of solar radiation. The colder, cloudier Northeast has a higher rate of breast cancer than the warmer, sunnier South. What's the connection? Exposure to sunlight helps the body manufacture vitamin D. Women in the Northeast manufacture less vitamin D because they are exposed to less natural sunlight, especially in the winter season. Here's how researchers made the connection. They graded a woman's exposure to the sun by the amount of skin damage she had suffered. Those with the most severe loss of elasticity in the skin had, paradoxically, the lowest risk of breast cancer! You might wonder why women didn't make up for the lack of vitamin D through sunlight by eating the right kinds of vitamin D-rich foods. A recent study from Massachusetts General Hospital showed that 59 percent of hospitalized patients had too little vitamin D in their bloodstream. That leads many experts to conclude that vitamin D deficiency is widespread in the general American population.
The Breast Cancer Prevention Diet by Robert Arnot MD, page 150

To put it bluntly; your life could depend on it. Sunlight may cause skin cancer, but there is also evidence that it could prevent a number of very common and often fatal diseases: breast cancer; colon cancer; prostate cancer; ovarian cancer; heart disease; multiple sclerosis; and osteoporosis. When combined, the number of people who die from these conditions is far greater than the number of deaths from skin cancer; which is why the current bias against sunlight needs, in my opinion, to be redressed, and why I would advise you to read this book.
The Healing Sun by Richard Hobday, page 11

There have been a number of scientific studies in the last 20 years that support the view that sunlight can inhibit cancer, and it is clear that the mortality and incidence of breast cancer and colon cancer in North America and other areas of the world increases with increasing latitude. In 1992, Dr Gordon Ainsleigh published a paper in the journal Preventive Medicine in which he reviewed 50 years worth of medical literature on cancer and the sun. He concluded that the benefits of regular sun exposure appear to outweigh by a considerable degree the risks of squamous-basal skin cancer, accelerated ageing, and melanoma. He found trends in epidemiological studies suggesting that widespread adoption of regular moderate sunbathing would result in approximately a one-third lowering of breast and colon cancer death rates in the United States. Colon cancer and breast cancer are the second and third leading causes of cancer deaths in North America and Dr Ainsleigh estimated that about 30,000 cancer deaths would be prevented each year if moderate sunbathing on a regular basis became the norm.
The Healing Sun by Richard Hobday, page 68

Interestingly, a country which is an exception to the link between low sunlight exposure and high incidence of colorectal and breast cancer is Japan. Even though people living in Japan are exposed to the low amount of sunlight, which is associated with these cancers in other areas, the incidence is very low in that country. This is undoubtedly because the Japanese eat a large quantity of fatty fish, which is rich in vitamin D.
Vitamin And Mineral Encyclopedia by Sheldon Saul Hendler MD PhD, page 98

Breast cancer is the most common form of cancer in women, causing about 370,000 deaths annually worldwide. Each year some 220,000 women in Europe and 180,000 women in North America are diagnosed with the disease. About 15,000 British women die of breast cancer annually, a death rate that is higher than elsewhere in Western Europe. One in 12 British women will develop breast cancer at some time in their lives and, as we have already seen, the incidence of breast cancer is increasing. The reasons for this are not altogether clear, but lack of sunlight could be a factor. In 1989 the Drs Garland, together with Dr Edward Gorham, published the first ever epidemiological work on the relationship between sun exposure and breast cancer (see Table 4). Their research demonstrated that, as in the case of colon cancer, there was a strong negative correlation between available sunlight and breast cancer death rates. The chances of women from areas of the United States with less available sunlight dying of breast cancer were 40 per cent higher than those of women who lived in Hawaii or Florida.
The Healing Sun by Richard Hobday, page 70

Since vitamin D can be toxic in doses that greatly exceed this value, researchers have developed synthetic analogues of vitamin D that retain the ability to inhibit cancer cell growth without the toxicity associated with high doses. These analogs have been successfully used in animal models of leukemia and breast cancer. Vitamin D may be related to other cancers. One study found that women who get low levels of sunlight experience high rates of breast cancer, suggesting that low vitamin D levels may play a preventive role in the disease. Low blood levels of vitamin D have been found in people with colon cancer.
Permanent Remissions by Robert Haas MS, page 132

As far as internal cancers are concerned, few physicians seem to have actually used sunlight therapeutically. One notable exception is the American physician Dr Zane Kime. In his book, sunlight Could Save Your Life, which was published in 1980, Dr Kime describes how he encouraged one of his patients with breast cancer to sunbathe. He took this rather unusual step following a consultation with a 41-year-old woman whose breast cancer had spread to her lungs and bones. She had already undergone a mastectomy and chemotherapy but to no avail. Dr Kime did not treat the cancer directly but instead, introduced a programme to improve the general health of his patient. She was only allowed to eat whole foods, and all of the refined polyunsaturated oils and fats were removed from her diet. She was also encouraged to spend time sunbathing; and the combination of diet and sunlight seems to have achieved remarkable results. Within a few months the patient was back at work and in the years that followed there were no apparent symptoms of her metastasized cancer. Unfortunately Dr Kime did not devote much of his book to this episode, nor did he state how many years of remission his patient enjoyed and, sadly, Dr Kime died in 1992.
The Healing Sun by Richard Hobday, page 75

SOURCE: Natural News.com