Q
Must you eat fat to absorb calcium and vitamin D?
Vitamin D is a fat-soluble vitamin, which is necessary for calcium absorption. Does that mean that there must also be fat in the gut in order to absorb calcium (i.e., that simply drinking nonfat milk on an empty stomach one would absorb neither the vitamin D nor the calcium)?
Asked by Anne-Marie Hislop • 493 votes
A
Fat does improve the body’s ability to absorb vitamin D, but for calcium, that is not the case, said Dr. Bess Dawson-Hughes, the director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.
The reason is that dietary fat stimulates the release of bile into the small intestine, which helps the digestion of fat and fat-soluble vitamins, such as vitamin D. Calcium, on the other hand, is not fat-soluble.
Dr. Dawson-Hughes demonstrated the importance of fat for vitamin D absorption in a recent study in The Journal of the Academy of Nutrition and Dietetics. In the study, 50 healthy men and women took a large dose of vitamin D3 — 50,000 international units — with breakfast, and then provided blood samples throughout the day.
Some of the subjects took the vitamin with a fat-free breakfast consisting of egg whites, fruit, toast and cranberry juice. The rest ate the same breakfast, but with either olive oil or corn oil mixed in so that it accounted for 30 percent of the calories. They tested two kinds of fat — monounsatured (olive oil) and polyunsaturated (corn oil) — to see if one type had a different effect than the other.
The subjects were also provided lunch and dinner with the same ratio of fat, protein and carbohydrate as their breakfasts.
At the end of the day, it was clear that dietary fat made a difference for vitamin D levels. The researchers found that the subjects in the fat groups had 32 percent greater absorption of the vitamin than those in the fat-free group. It made no difference whether the fat was olive or corn oil.
Previous studies have shown that calcium carbonate, the form of calcium most commonly used in supplements, is better absorbed when taken with a meal, regardless of its fat content. But for calcium citrate, a less common form of the mineral, there is no evidence that taking it with a meal has any effect on its absorption, Dr. Dawson-Hughes said.