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. [6
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