Higher vitamin D levels significantly drive down colorectal cancer risk, a large new international study has found.
The vitamin, found in fatty fish and sunshine, was found to strengthen resistance to stomach tumors by blocking a common gateway that cancer cells pass through – and it was most protective in women.
The report, led by the Harvard TH Chan School of Public Health, adds weight to a long-suspected theory which, until now, had not been proven.
It also suggested the ideal amount of vitamin D we should be aiming for may be higher than current guidelines suggest.
This study is yet another reminder to prioritize loading up on vitamin D, since around three quarters of Americans and a fifth of Brits are deficient – but while the vitamin is hard to find in natural foods, experts warn to scrutinize supplements that may not have been tested rigorously.
Vitamin D is hard to find in high concentrations in natural foods, but it can be ingested from fatty fish like salmon, cheese, fortified milk, mushrooms, and eggs
CAN YOU RELY ON VITAMIN D SUPPLEMENTS?
by Tim Spector, Professor of Genetic Epidemiology at King’s College London, for The Conversation
Surprisingly, there is a lack of evidence to support the health benefit claims of virtually all vitamin supplements on the market.
One study based on the large SELECT trial suggested that supplements such as vitamin E and selenium actually increased prostate cancer in some men. And in 2015, massive analyses combining 27 studies on half a million people concluded that taking vitamin and mineral supplements regularly failed to prevent cancer or heart disease.
Not only are they a waste of money for the majority of us – but if taken in excessive quantities they can actually hasten an early death, increasing your risk of heart disease and cancer.
Virtually no vitamins or supplements have actually been shown to have any benefit in proper randomised trials in normal people without severe deficiencies.
Rare exceptions have been lutein nutrients for macular degeneration, a common cause of blindness – and vitamin D, the golden boy of vitamins.
Since the 1980s, researchers (including myself) have written thousands of papers, associating a lack of our favourite vitamin with over 137 diseases. A 2014 BMJ report, however, found these links mainly to be spurious.
Until now we have believed that taking vitamin supplements is ‘natural’ and my patients would often take these while refusing conventional ‘non-natural’ drugs.
Our body may not view supplements in the same misguided way.
Vitamin D mainly comes from UV sunlight converted slowly in our skin to increase blood levels or is slowly metabolised from our food.
In contrast, taking a large amount of the chemical by mouth or as an injection could cause a very different and unpredictable metabolic reaction. For example, our gut microbes are responsible for producing around a quarter of our vitamins and a third of our blood metabolites and also respond to changes in vitamin levels picked up by receptors in our gut lining. Any artificial addition of large amounts of chemicals will upset some sensitive immune processes.
The news that even my favourite vitamin can be dangerous is a wake-up call.
We should be taking our worldwide abuse of these chemicals much more seriously rather than routinely adding them to foods.
‘In the past, substantial differences between assays made it difficult to integrate vitamin D data from different studies,’ explained Regina G. Ziegler, PhD, a National Cancer Institute epidemiologist and co-senior author of the study.
‘This calibration approach enabled us to systematically explore risk over the broad range of vitamin D levels seen internationally.’
The study, published online today in the Journal of the National Cancer Institute,
Vitamin D, known for its role in maintaining bone health, is hypothesized to lower colorectal cancer risk via several pathways related to cell growth and regulation.
Previously, studies have been inconclusive about the cancer-fighting benefits of higher concentrations of circulating 25-hydroxyvitamin D, the accepted measure of vitamin D status.
There have only been a handful of randomized clinical trials on vitamin D supplements and colorectal cancer – none of which found a connection.
The authors of the new study say that may be because the studies were too small, the supplements weren’t taken for long enough, or the subjects didn’t fully comply – because now, they claim, they have the clearest evidence yet that there is a concrete link.
To find it, researchers conducted an analysis of more than 5,700 colorectal cancer cases and 7,100 controls from the United States, Europe, and Asia.
Compared to participants with circulating vitamin D concentrations considered sufficient for bone health, those with a vitamin D deficiency had a 31 percent higher risk of colorectal cancer during follow-up five years later.
Strong bone health, which is affected by vitamin D levels, was also associated with a 22 percent lower risk.
These links persisted even after adjusting for known colorectal cancer risk factors.
The protection was seen in all groups, but particularly in women.
The lifetime risk of colorectal cancer is 4.2 percent (one in 24) in women and 4.5 percent (one in 22) in men.
Colorectal cancer is the third most common cancer and third leading cause of cancer-related deaths in both men and women in the United States, with about 140,250 new cases and 50,630 deaths expected during 2018.
‘Currently, health agencies do not recommend vitamin D for the prevention of colorectal cancer,’ said Marji L. McCullough, ScD, American Cancer Society epidemiologist and co-first author of the study.
‘This study adds new information that agencies can use when reviewing evidence for vitamin D guidance and suggests that the concentrations recommended for bone health may be lower than would be optimal for colorectal cancer prevention.’