Absorbing high levels of vitamin D has been linked to a lower risk of developing cancer, according to a study published by the British Medical Journal (BMJ).

Vitamin D is made by the skin in response to sunlight. While research has already found that vitamin D can help combat bone diseases – due to its ability to main calcium levels, keeping bones, teeth and muscles healthy – this is a new development in the vitamin’s capabilities.

Researchers found that a higher level of vitamin D was associated with a lower (around 20%) relative risk of overall cancer in both men and women. In particular, they found a lower 30-50% relative risk of liver cancer.

The new research involved 34,000 Japanese men and women aged between 40 to 69 years, who were split into four groups depending on their vitamin D levels.

Researchers monitored participants for an average of 16 years, during which time 3,301 new cases of cancer were recorded. Higher vitamin D levels were also associated with a lower (30-50%) relative risk of liver cancer, and the association was more evident in men than in women. 

Prior to this study, most research has have been carried out in European or American populations, and evidence from Asian populations is limited. Vitamin D concentrations and metabolism can vary by ethnicity, so it was important to find out whether similar effects would be seen in non-Caucasian populations.

The researchers point to some study limitations, for example numbers of organ specific cancers were relatively small. And while they adjusted for several known risk factors, they cannot rule out the possibility that other unmeasured factors may have influenced the results, making it difficult to draw firm conclusions about cause and effect.

Commenting on the study, Sophia Lowes from Cancer Research UK echoed this, adding: “It’s not clear whether being deficient in this vitamin just reflects poor general health rather than having a direct impact on cancer risk.

“Enjoying the sun safely, while taking care not to burn and increase skin cancer risk, should help most people get enough vitamin D in summer.” 

The authors say their findings support the theory that vitamin D may protect against the risk of cancer, but that there may be a ceiling effect, which may suggest that there are no additional benefits beyond a certain level of vitamin D.

“Further studies are needed to clarify the optimal concentrations [of vitamin D] for cancer prevention,” they conclude.