Vitamin D and the Risk of Bowel Cancer 

This blog was written by Dr Issraa Al-Obaidi (University of Strathclyde)

Colorectal cancer is the most common type of cancer in the UK. It is also known as bowel cancer, colon cancer and rectal cancer. The main symptoms of this disease are diarrhoea or constipation, abdominal pain, blood in the stool, unexpected weight loss and fatigue. A recent report for England indicates that this disease has increased in younger adults under the age of 50. 

A study conducted by Hanseul Kim and colleagues at Harvard found that young people (women in this particular study) were recorded at risk of early onset colorectal cancer due to vitamin D deficiency.  This vitamin is formed naturally under our skin when we are outside exposed to sunlight, so it is called sunshine vitamin. It keeps our bones, teeth, and muscle healthy by working together with calcium and phosphorous (a mineral found in foods like beer, cheese, beans, and fish). Vitamin D is available in our daily food such as milk, fish (salmon, tuna, trout), egg yolk, cheese, some cereals and liver. Any deficiency in vitamin D can cause muscle cramps, bone pain, fatigue, and mood changes such as depression. Your GP can order a blood test for you to check any deficiency of vitamin D in your body.

There are two types of vitamin D; D2 and D3 which both need to be converted by liver and then by kidney to the main form of that vitamin to be useful for our body, however D3 or called cholecalciferol seems to be more effective than D2 to our body. Since this vitamin is lipid soluble, it is absorbed with fatty food in our diet.

This new study found that daily eating of foods containing vitamin D can reduce the risk of pre-cancerous polyps (small growths on the lining of the colon) and early onset of colorectal cancer in people under 50, while no correlation between the disease and vitamin D deficiency after the age of 50 was found. A review about colon cancer and vitamin D explains that vitamin D acts as anti-inflammatory agent that reduce the risk of inflammatory bowel disease which is one of the most predominant high-risk conditions for colon cancer. Vitamin D is associated with better overall survival of colon cancer patients as well. As a consequence, vitamin D prevents the development and progression of colon cancer.

300IU of vitamin D (or 7. 5micrograms) may cut the risk of this type of cancer to half. If our daily foods or exposure to sunlight were not enough to get this vitamin, the NHS recommends young adults to have 10 micrograms (or sometimes called 400IU) supplement daily specially in autumn and winter. 

How did the media do with coverage of this research? 

The Express provided a clear description of Hanseul Kim and colleagues’ work and quoted directly from the research team who had conducted the study. Their headline ‘Bowel cancer: vitamin D deficiency could increase risk particularly among the young’ accurately reflected the study findings. Other media sources used more sensationalist headlines, which is very common in reports around nutrition and health as we have described previously in posts about diet, dementia and cancer. For example the Daily Mail ran with a headline of ‘eating just half a serving of salmon a day can slash your risk of getting bowel cancer by 50%, study claims’ in reference to the findings of this study. In our ‘How to Research the Headlines’ tips series we have described the importance of referring to the absolute risk or benefit when describing results, so including the benefit with and without eating this portion of food. As with all new research on nutrition, it is important to weigh up the good and bad effects of a food, for example, as discussed in a previous blog; while it has been shown that eating cheese may slow down cognitive decline, a high fat diet is not good for heart health. However, it seems taking a daily vitamin D supplement has no draw backs. Just remember to check the supplement is 10 micrograms (400IU) to get the full benefit.