In a recent study, scientists found folate, magnesium, and dairy products may all help stave off bowel cancer. But there is no evidence that garlic or onions, fish, tea or coffee protect against the disease.
In the US alone around 1 in every 20 people is likely to develop bowel cancer at some point during their lifetime.
While deaths from the disease have been falling in most developed countries, the numbers of new cases have been rising in some, including in Canada, the UK, and the Netherlands.
Screening for the disease can pick up the disease at an early treatable stage, but take-up varies considerably from country to country.
And as it takes more than 15 years for bowel cancer to develop, a healthy lifestyle likely has a key role in helping to halt or stop its progress altogether.
In the study, researchers reviewed published findings to see the impact of dietary and medicinal factors on bowel cancer risk.
The medicinal factors included: aspirin; non-steroidal anti-inflammatory drugs (NSAIDs), such as paracetamol; and statins.
The dietary factors included: vitamins or 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.
Some 80 articles out of a total of 343 were included in the overarching (umbrella) analysis of pooled data analyses.
The team found that aspirin was likely protective against bowel cancer, lowering the risk by between 14% and 29% at doses as low as 75 mg/day, with a dose-response effect reported up to 325 mg/day.
NSAID use for up to 5 years was linked to a significant (26% to 43%) fall in the incidence of bowel cancer.
Magnesium intake of at least 255 mg/day was linked to a 23% lower risk compared with the lowest intake, and high intake of folic acid was linked to a 12-15% lower risk.
Similarly, eating dairy products was linked to 13% to 19% lower risk of the disease.
Fibre intake was linked to a 22%-43% lower risk, while fruit/vegetable intake was linked to up to a 52% lower risk, with added benefit for every additional 100 g/day increase in intake.
Dietary soy intake was linked to a modest, but significant, fall (8-15%) in risk.
But there was no evidence that vitamins E, C, or multivitamins were protective. Similarly, there was no evidence that β-carotene or selenium helped stave off the disease.
The data were weak or equivocal on the impact of tea; garlic or onions; vitamin D either alone or combined with calcium; coffee and caffeine; fish and omega 3; and inconsistent on the protective effect of vitamin A and the B vitamins.
A modest protective effect was found in studies for high calcium intake, but a meta-analysis of clinical trial data found no protective effect, and even an increased risk.
Similarly, although studies suggest that statins may lower cancer risk, no positive effect was noted in meta-analyses of clinical trial data.
Most of the available studies reported an increased risk of between 12% and 21% for meat, particularly red and processed meat. Dose-effect studies reported a 10-30% increased risk for each additional 100 g/day of red meat eaten.
Alcohol was linked to a significantly increased risk. The higher the intake, the greater the risk. This was evident even at the lowest level of consumption studied: 1-2 drinks/day.
The team suggests that their findings could help clinicians advise patients on the best diet to lower bowel cancer risk and guide the direction of future research.
If you care about bowel health, please read studies about why some people more likely to have bowel diseases, and scientists find a new treatment for inflammatory bowel disease.
For more information about health, please see recent studies about a big cause of irritable bowel syndrome, and results showing this food may worsen inflammatory bowel diseases.
The study was published in Gut.
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