Halve your risk of colon cancer The vitamin D and cancer connection, first proposed by Dr Cedrick Garland in 1980, led to research that showed a strong association between risk of colon cancer and dietary intake of vitamin D and calcium.  An eight year study of 25,802 people from the state of Maryland in the USA found that those with blood levels of vitamin D equivalent to 10mcg (400iu) or more had half the risk of colon cancer compared to those with lower levels.  This is twice the US RDA of 5mcg (200iu).
In the UK, there is no recommended daily dietary intake for vitamin D if you are aged between four and 50 and live a ‘normal life-style’. However, ‘normal’ means spending time every day outdoors in the sunshine, which is not always possible given the UK weather and people’s lifestyles. For those confined indoors, experts recommend 10mcg per day.  Since 1980, many researchers have confirmed Dr Garland’s hypothesis. A scientific review undertaken by the National Cancer Institute in 2007 found that vitamin D was beneficial in preventing colorectal cancer. Although the study found no link between vitamin D status and overall cancer mortality, the study did show that blood levels of 80 nanomoles per litre (nmol/L) or higher were associated with a 72% reduction in colorectal cancer mortality.  As you’ll see later, to achieve blood levels of 80nmol/L, you need to have just over 25mcg (1,000iu) a day.
Similar blood levels and vitamin D intake were found to protect against colon cancer in a study that followed 1,500 people for 25 years. At 80nmol/L the rate was cut by 50%, whereas levels of over 100nmol/L reduced colon cancer incidence by 66%, according to research published in the American Journal of Preventative Medicine. When five studies were ‘pooled’ together, researchers found that a 50% lower risk of colorectal cancer was associated with a blood level of greater than, or equal to, 83nmol/L, compared to less than or equal to 30nmol/L. They concluded that 1,000-2,000iu per day of vitamin D could reduce the incidence of colorectal cancer with minimal risk. 
Reduce your risk of breast and ovarian cancer by a third Several teams of researchers have found that adequate levels of vitamin D also lower the chances of developing breast cancer. Low blood levels of vitamin D have been correlated with breast cancer disease progression and the spread of cancer to the bones.  Women with advanced breast cancer that had spread to their bones were less likely to die of the disease when they had high amounts of active vitamin D in their blood.  A team of cancer prevention specialists at the University of California, San Diego, found that women with the highest level of vitamin D in their blood had a 50% lower risk of breast cancer than those with the lowest level.  “The results were very clear,” said co-author Dr Cedric Garland. “The higher your level, the lower the risk.” To have a blood level that would cut your risk by 50%, the researchers said that you would have to take 50mcg (2,000iu) daily and also spend 10-15 minutes in the sun.
Researchers from the same university also reviewed 63 studies, published worldwide between 1966 and 2004, and found that taking 25mcg (1,000iu) of the vitamin daily could lower an individual’s cancer risk by 50% in colon cancer, and by 30% in breast and ovarian cancer. [10a] [10b] In fact, Dr Garland has estimated that 600,000 cases a year of breast and colorectal cancer could be prevented by adequate intakes of vitamin D.  Protection from prostate cancer Vitamin D also helps protect men from prostate cancer. A team led by a researcher from Harvard Medical school followed 15,000 men and found that those who had below average levels of the vitamin in their blood had a “significantly increased risk of aggressive prostate cancer”.
In this study, published in PLOS Medicine, 50nmol/L counted as deficient and even 80nmol/L was described as ‘sub-optimal’. Taking the US Recommended Daily Allowance (RDA) of vitamin D (10mcg, or 400iu/day) was found to reduce the risk of pancreatic cancer by 43% in a sample of more than 120,000 people from two long-term health surveys.  The Harvard researchers said further work was necessary to determine if consuming vitamin D in the diet, or through sun exposure, might have even more of an effect than taking supplements. How does vitamin D work? The anti-cancer activity of vitamin D is thought to result from its role in a wide range of mechanisms central to the development of cancer, such as regulating cell growth, and apoptosis (programmed cell death). 
Programmed cell death is a normal process that should happen in our bodies if a cell is damaged in any way. This is one of the problems with cancer – the damaged cell continues to replicate. One clinical study of 92 colon cancer patients showed that supplementing the diet with calcium and vitamin D appeared to increase the levels of a ......
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