Even the lowest possible dose of aspirin (75 mg) can ward off bowel cancer, if taken regularly, finds research published online in the journal Gut.
This protective effect is apparent after just one year and in the general population, not just those considered to be at risk of developing the disease, which is the second most common cause of cancer death in the world, killing almost half a million people every year.
Although previous research has shown that aspirin protects against bowel cancer, it is not known what the most effective dose is and how long it needs to be taken for.
The research team investigated just under 2,800 people with bowel cancer and just under 3,000 healthy people, matched for age, sex, and residential locality.
All participants completed food frequency and lifestyle questionnaires to assess their usual diet and lifestyle choices, which are known to influence bowel cancer risk.
NSAID (non-steroidal anti inflammatory drug) intake was categorised as taking more than four tablets a month of low dose aspirin (75 mg), other NSAIDs, or a mix.
The likelihood of surviving bowel cancer once diagnosed or developing the disease anew was then tracked over five years.
In all, 354 (15.5%) of those with bowel cancer were taking low dose aspirin compared with 526 (18%) of their healthy peers.
Taking any NSAID regularly, curbed the chances of developing bowel cancer compared with those who didn't take these painkillers.
This finding held true, irrespective of lifestyle choices, age, diet, weight, and level of deprivation
After a year, taking daily low dose aspirin was associated with a 22% reduced risk of developing bowel cancer, and the magnitude of the reduction in risk was cumulative, rising to 30% after five years.
Some 1,170 people died out of a total of 3,417 people diagnosed with bowel cancer (including those who were healthy at the start of the study) during the monitoring period. Most of these deaths (1,023) were attributable to the disease.
Information on NSAID intake was available for 676 of these 1,023 deaths, and it showed that taking NSAIDs of any kind did not influence the risk of death from any cause nor did it increase bowel cancer survival.
But, crucially, the findings show that high doses of aspirin, taken for a long time, are not needed to help ward off bowel cancer, say the authors.
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