By: Forrest Nielsen
While it is clear that both calcium and vitamin D are important dietary essentials for good health, until recently there was insufficient scientific agreement on how much of each should be recommended.
That changed in November, when an expert panel of the Institute of Medicine of the U.S. National Academy of Sciences announced estimated recommended dietary allowances for these nutrients. Bone health was the major factor for setting the RDAs for calcium and vitamin D.
The RDA, which is the daily intake that meets the requirement of almost all individuals, was set at 1,100 milligrams per day for men ages 19 to 70 and women 19 to 50. For older individuals, the RDA was set at 1,200 milligrams per day. These values were determined in large part on the basis of research with human volunteers conducted at the Grand Forks Human Nutrition Research Center.
The RDA for vitamin D was set at 600 International Units for adults of all ages.
Most Americans get most of their calcium from foods, with some 43 percent of all people and 70 percent of postmenopausal women getting calcium from supplements.
However, many individuals may not have adequate intakes of calcium without taking supplements. In a recent study conducted at the GFHNRC, we estimated the amount of calcium consumed from foods among women aged 40 years and older. The study showed that 203 out of the 224 women did not meet the RDA without taking supplements.
The main sources of calcium in most diets are dairy products. Other sources can be foods fortified with calcium, such as orange juice and ready-to-eat cereals. In light of the widespread use of calcium supplements and calcium-fortified foods, the IOM cautioned against taking too much calcium. At intakes greater than 2,000 milligrams per day, IOM noted increased risk for kidney stones and blood vessel calcification that can result in stroke or heart attacks.
Unlike calcium, vitamin D also can be made by the skin upon exposure to sunlight. The IOM set the RDA for vitamin D to support adequate blood levels of the vitamin under conditions of minimal sun exposure. The fact is that most Americans, particularly those of us living in the northern latitudes, have insufficient exposure to the amounts of sunlight needed to support optimal blood levels of vitamin D — without getting dietary sources of the vitamin. Sun exposure may be limited due to clothing, indoor work and lifestyles and use of sunscreens to prevent skin cancer.
After evaluating the diets of the women studied at the GFHNRC, we found their average intake of vitamin D to be 135 IU per day — none met the RDA. This suggests that most people in North Dakota are at risk for low vitamin D status if they are not taking supplements or consuming vitamin D-fortified foods such as milk, orange juice and ready-to-eat cereals.
Low vitamin D status is particularly of concern for older people, as it has been linked to an increased risk for cancers of the breast, lung, colon and prostate; multiple sclerosis; diabetes; high blood pressure, arthritis and stroke; and poor cognition.
However, as the IOM observed, high intakes of vitamin D (more than 4,000 IU per day) are linked to kidney damage and blood vessel calcification that can lead to heart disease.
Many people in North Dakota appear to have intakes of calcium and vitamin D that do not meet the RDAs and may be at increased risk for such chronic diseases as osteoporosis, heart disease and cancer. This means that it is prudent to choose a diet that includes good sources of these nutrients, particularly if dietary supplements are not used.