Posted on Tue, 13 Mar 18
Researchers expected to find that calcium supplements would prevent the formation of precancerous colorectal polyps. To their surprise, they found the opposite.
Previous studies have generally found that dietary calcium is associated with a lower risk of precancerous colorectal polyps, so when researchers set out to study the impact of calcium supplements they expected to see a benefit. They didn’t.
In their study, the researchers examined data from 2259 people, aged 45 to 75 years, with previous history of adenoma. The participants had been given either 1) 1200 mg per day of elemental calcium carbonate, 2) 1000 IU per day of vitamin D3, 3) calcium plus vitamin D, or 4) placebo.
Participants took the dietary supplements or placebo for 3 or 5 years and then underwent a colonoscopy. They were assessed again 3 to 5 years after stopping supplementation.
During the initial treatment there was no influence of calcium and/ or vitamin D on risk, however, 3 to 5 years after stopping supplementation it was found that calcium alone and calcium plus vitamin D increased risk for sessile serrated adenomas or polyps (SSA/Ps), but not for serrated polyps in general or hyperplastic polyps.
Analysis of their data suggested that women and current smokers had higher risks of serrated polyps when exposed to supplemental calcium. There was no association between Vitamin D alone or dietary calcium and SSA/Ps.
Although dietary calcium has been associated with a lower risk of precancerous colorectal polyps, it is biologically plausible that supplemental calcium could increase risk. A calcium regulated protein is highly expressed in SSA/Ps, point out the researchers involved in this study.
So, should people stop taking calcium and vitamin D supplements? Well, no, the potential benefit far outweighs risk.
To place this study in context, this research was in people with a previous tumor, so is not generalisable to everyone. Also, SSA/Ps are relatively rare with a prevalence of 2% to 7% in adults and as little as 1% of those potentially progressing to cancer . The number of people in this high-risk group who had SSA/Ps was 6%.
Commenting on this study, Professor Kevin Whelan, Head of Department of Nutritional Sciences, King’s College London said “it is important to highlight that this study was performed in people who already had a history of bowel polyps and therefore we cannot assume that calcium supplements would have the same effects in healthy people who have never had polyps. More research is needed to understand the effect of calcium on the risk of polyps in the general healthy population.”
“Calcium supplements are important for the health of our bones and studies show that those who take supplements have a reduced risk of bone fracture,” he added. “Therefore, the results of this study in people already at risk of bowel polyps should not result in the public changing their intakes of calcium at this time .”
It is also important to note the dose of calcium may have been unnecessarily high. Usual dietary intakes of calcium were at least 600 mg per day, which with the addition of the dietary supplements would have increased participants intake to at least 1800 mg per day, higher than the threshold for adequate calcium intakes of 1000-1500 mg after which no additional benefit for bone health is expected to occur .
If you are taking calcium supplements you could consider calculating how much you require to achieve an optimal daily intake with a Calcium Calculator, so you are not taking too much. You could also consider using calcium hydroxyappetite, a far more effective form of calcium than calcium carbonate which works better even at a lower dose . And if you have a previous history of colorectal cancer or are at increased risk your best option may be to ensure adequate daily intake of calcium with food.
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