Enough Isn’t Enough: An epidemic of vitamin D deficiency

Many U.S. women of childbearing age, particularly those of African descent, lack sufficient vitamin D even though they consume the recommended amount, a new study suggests. Symptoms of vitamin D deficiency can be subtle among adults, but infants born to these women could be marked for major health problems.

Vitamin D is an essential nutrient for proper bone growth, and children who get too little can develop rickets, a skeletal disease. A newborn’s quotient of the vitamin is largely determined by the concentration in the mother’s blood.

Recent research has identified rickets, once nearly conquered in the United Sates, as a reemerging problem among African American children. The findings raised scientists’ concerns that the children’s mothers may be lacking in vitamin D.

There’s also some evidence that insufficient vitamin D makes people vulnerable to certain forms of cancer and diabetes.

Human skin produces vitamin D when exposed to sunlight. People also obtain the nutrient by consuming vitamin supplements, fish oil, and breakfast cereals and milk fortified with vitamin D.

However, heavily pigmented skin is less efficient than light skin at synthesizing vitamin D from sunlight. Furthermore, many nonwhite people can’t easily digest the lactose in dairy products, so they limit their milk consumption and thus vitamin D intake.

To investigate the incidence and causes of vitamin D deficiency, researchers at the Centers for Disease Control and Prevention in Atlanta reviewed the health and eating habits of white and black nonpregnant U.S. women, ages 15 to 49. The team used data from a national nutritional survey conducted between 1988 and 1994.

The researchers considered the women’s blood concentrations of a component of vitamin D called 25-hydroxyvitamin D, or 25(OH)D, and how often they consumed milk, cereal, and dietary supplements. The researchers also analyzed indicators of each woman’s exposure to sunlight and several other factors that can affect 25(OH)D concentration in blood.

In the July American Journal of Clinical Nutrition, Kelley S. Scanlon and her colleagues report that 42 percent of the 1,546 African American women in the study had 25(OH)D concentrations below 15 micrograms per liter (g/l), which some past studies have identified as marking vitamin D deficiency. Of the 1,426 white women in the study, only 4.2 percent had 25(OH)D concentrations below that threshold.

The recommended daily intake of vitamin D for adult women is 5 g. Among black women getting one to two times the recommended daily dose from supplements, and potentially more from other food and sunlight, 30 percent had a low 25(OH)D blood concentration.

The new data “provide irrefutable evidence that vitamin D deficiency is a major unrecognized epidemic in adult women of childbearing age,” argues Michael F. Holick of Boston University. In an article accompanying the new study, he says that the adequate intake of vitamin D for adults who don’t get significant exposure to sunlight should probably be at least four times the currently recommended amount.