“There are certain risk factors that don’t allow people to process vitamin D as well,” said DOR research scientist Nancy Gordon, lead author of the study, which was published recently in Nutrition Journal. “These include having darker skin color, being obese and older, and having health problems that interfere with the metabolism of vitamin D.”
Clinical guidelines from The Permanente Medical Group (TPMG) state that most people need a daily vitamin D supplement to maintain optimum blood serum levels of this essential nutrient.
More than 8,800 women and 7,100 men answered questions about their use of dietary supplements as part of Kaiser Permanente Northern California’s 2008 Member Health Survey, which is conducted every three years to estimate the prevalence of health conditions and health-related behaviors among adult members.
Vitamin D insufficiency can lead to osteoporosis and rickets (brittle and misshapen bones). Epidemiological studies have also identified an increased risk of chronic diseases such as cancer, diabetes, hypertension, and cardiovascular disease, as well as autoimmune disorders, respiratory illnesses, and pregnancy-related problems, but clinical trials are needed to determine whether the risk of any of these conditions can be decreased by raising vitamin D in blood serum to sufficient levels.
Sources of vitamin D
Vitamin D is obtained from exposure to the sun; foods, especially fish such as salmon, tuna and swordfish, and milk and orange juice fortified with vitamin D; and dietary supplements. Blood serum tests have shown that a substantial percentage of the U.S. population has vitamin D levels below current recommended daily allowances.
“People are not getting vitamin D from the traditional ways ¬of food and sun,” said co-author Bette Caan, DOR research scientist. “Dietary supplements are a way to meet vitamin D requirements.”
The 2008 Member Health Survey asked Kaiser Permanente Northern California members whether they were taking a multivitamin, calcium plus vitamin D, and/or a singular vitamin D supplement.
The study identified low levels of vitamin D supplementation overall, and a significant disparity between genders: 40% of women and 54% of men between 25 and 50 years old, and 27% of women and 46% of men between 51 and 85 years old, got no vitamin D from dietary supplements. The TPMG Chiefs of Endocrinology recommend a vitamin D supplementation dose of 1,000 to 2,000 IU per day in all adults to maintain an optimal vitamin D level, with some adults requiring up to 4,000 IU per day. This is higher than the Institutes of Medicine (IOM) recommendation of 600 IU per day for children and adults up to age 70 and 800 IU per day for adults over age 70.
“The age and gender-related differences in vitamin D supplementation are primarily due to significantly greater use of calcium plus D by women over age 50,” wrote Gordon, Caan and co-author Maryam M. Asgari, also a DOR research scientist. Calcium plus vitamin D supplements are often recommended by physicians to prevent osteoporosis, which is more common among older women than men.
National nutrition surveys have found higher levels of vitamin D deficiency among blacks and Latinos compared with whites. The Member Health Survey found that black and Latino women are less likely than whites to be getting vitamin D from dietary supplements. They also identified ethnic and racial disparities in vitamin D supplementation among obese, diabetic and hypertensive adults, conditions that may be affected by insufficient vitamin D levels.
In the 25 to 50 age group, black (48%) and Latina (47%) women were significantly more likely than white women (35%) to be getting no vitamin D from dietary supplements; the results in the 51 to 85 age group were similar, with 37% of black, 35% of Latina and 26% of white women not taking vitamin D supplements. In both age groups, black women were half as likely as white women to be getting vitamin D from both multivitamins and calcium with D supplements.
Among women who were obese, diabetic and hypertensive, blacks (47%, 48% and 39%, respectively) and Latinas (55%. 54% and 41%, respectively) were significantly more likely than non-Hispanic whites (34%, 31% and 29%, respectively) to get no vitamin D from dietary supplements.
For men aged 51 to 85, black (54%), (59%) and Chinese (57%) men were significantly more likely to get no vitamin D from supplements than white men (44%). Likewise, Latino men who were obese (60%), diabetic (60%) or hypertensive (56%) were significantly less likely to get vitamin D from supplements than white men (51%, 45% and 44%, respectively).
Lead author Gordon pointed out that vitamin D supplementation has been recommended by some health disparities researchers as an easy and relatively inexpensive way to help reduce racial and ethnic health disparities and contain health care costs due to chronic diseases. “Vitamin D doesn’t cost very much and it’s not toxic at the correct doses,” Gordon opined. “So it would seem that there is little risk of harm and potentially great benefit in recommending it, especially to those with known risk factors for vitamin D deficiency.”
The Member Health Survey is funded by the Kaiser Permanente Northern California Community Benefit Program.