Folate, magnesium and dairy products may all help ward off colon cancer, but there's no evidence that garlic or onions, fish, tea or coffee protect against the disease, finds an overarching analysis of published studies.
Since it takes more than 15 years for colon cancer to develop, a healthy lifestyle likely plays a key role in helping to prevent or stop its progress altogether, say the researchers.
For the study, the team looked at 80 different analyses of clinical trials and observational studies that had assessed the impact of dietary and medicinal factors on bowel cancer risk.
The dietary factors included vitamins, minerals and supplements (magnesium, calcium, folic acid, vitamin A, B, C, E, D, β-carotene and selenium), coffee, tea, fish and omega-3 fatty acids, dairy products, fibre, fruit and vegetables, meat, and alcohol.
The medicinal factors included aspirin, non-steroidal anti-inflammatory drugs (NSAIDs) and statins.
Magnesium, folate, fibre protective
People who consumed at least 255 milligrams of magnesium each day were 23% less likely to be diganosed with colon cancer compared to people who consumed the least. Magnesium intake was assessed from diet and supplements.
Excellent sources of magnesium include spinach, Swiss chard, quinoa, oat bran, salmon, mackerel, black beans, navy beans, chickpeas, kidney beans, tempeh, pumpkin seeds, sunflower seeds, hemp seeds, almond butter and cashews.
A higher intake of the B vitamin folate was also associated with a lower risk. You'll find plenty of folate in lentils, black beans, chickpeas, cooked spinach, asparagus, Brussels sprouts, broccoli, avocado and artichokes.
As well, consuming more fibre was tied to a lower risk of colon cancer. And participants who ate the most fruit and vegetables - versus the least - had half the risk of developing the cancer.
Soy intake was associated with a modest, but significant, reduction in risk.
Similarly, eating dairy products was associated with a modestly lower risk of the disease. But the small number of available studies and the variety of dairy products included make it difficult to draw firm conclusions about the how mach dairy may guard against the disease.
There was no evidence that vitamins E, C, or multivitamins were protective. Similarly, there was no evidence that β-carotene or the mineral selenium helped prevent the disease.
The data were weak for the impact of tea, garlic or onions, vitamin D either alone or combined with calcium, coffee and caffeine, fish and omega-3 fats.
Red meat, alcohol tied to increased risk
Most of the available analyses of observational studies reported an increased risk for meat, particularly red and processed meat. The more red meat consumed, the greater the risk.
Alcohol was associated with a significantly increased risk of colon cancer. This was evident even at the lowest level of consumption studied: 1-2 drinks/day.
Medications and risk
The results suggested that aspirin is likely protective against bowel cancer. NSAID use for up to five years was associated with a significant (26% to 43%) fall in the incidence of colorectal cancer.
Limitations
The researchers caution that the level of evidence is low in most cases, mainly due to wide differences in study designs, end points and numbers of participants.
Nevertheless, they suggest that their findings could help clinicians advise patients on dietary recommendations to help reduce colon cancer risk and guide the direction of future research.
Source: Gut, September 28, 2020.
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