The sunshine vitamin: are vitamin D levels linked with better survival in colorectal cancer patients?

The authors reviewed previous studies to assess whether there is a link between vitamin D levels in patients and the outcome of cancer.

Vitamin D is produced by the skin during exposure to sunshine and is also taken in through diet or supplements. Foods high in vitamin D include tuna, salmon, beef liver, fortified cereals and egg yolks.

Vitamin D levels are estimated based on blood levels of 25-hydroxyvitamin D [25(OH)D]. Less than 3% of colorectal cancer patients have sufficient levels of vitamin D.  A blood 25(OH)D level between 50 to 75 nmol/L is defined as vitamin D insufficiency. A level less than 50 nmol/L indicates vitamin D deficiency. Previous studies have suggested that blood levels of vitamin D may affect the outcome of colorectal cancer. However, this remains a matter of debate and requires further clarification.

This study reviewed 25 papers that examined the links between vitamin D and the outcome of patients with cancer. Five of the studies specifically evaluated the link between vitamin D levels in colorectal cancer patients. In each study vitamin D levels were estimated at or near the time of each patient’s diagnosis. Overall survival (time until death from any cause) and cancer-specific survival (time until death from colorectal cancer) were assessed for each patient.

Colorectal cancer patients were divided into 4 groups based on their levels of vitamin D: high, medium, low, or very low. The risk of death from any cause was 45% lower for patients with the highest levels of vitamin D, compared to those with the lowest levels. The risk for cancer-specific death was 35% lower for patients with the highest levels of vitamin D, compared to those with the lowest levels. 

The authors concluded that cancer patients with higher vitamin D levels at diagnosis have improved overall-survival and better disease-free survival. 

These results were only based on observation. Further research is needed to determine whether vitamin D supplements can improve patient outcomes.