Medical Progress – Vitamin D Deficiency
Definition and Prevalence of Vitamin D Deficiency
Although there is no consensus on optimal levels of 25-hydroxyvitamin D as measured in serum, vitamin D deficiency is defined by most experts as a 25-hydroxyvitamin D level of less than 20 ng per milliliter (50 nmol per liter).7-10 25-Hydroxyvitamin D levels are inversely associated with parathyroid hormone levels until the former reach 30 to 40 ng per milliliter (75 to 100 nmol per liter), at which point parathyroid hormone levels begin to level off (at their nadir).10-12 Furthermore, intestinal calcium transport increased by 45 to 65% in women when 25-hydroxyvitamin D levels were increased from an average of 20 to 32 ng per milliliter (50 to 80 nmol per liter).13 Given such data, a level of 25-hydroxyvitamin D of 21 to 29 ng per milliliter (52 to 72 nmol per liter) can be considered to indicate a relative insufficiency of vitamin D, and a level of 30 ng per milliliter or greater can be considered to indicate sufficient vitamin D.14 Vitamin D intoxication is observed when serum levels of 25-hydroxyvitamin D are greater than 150 ng per milliliter (374 nmol per liter).
With the use of such definitions, it has been estimated that 1 billion people worldwide have vitamin D deficiency or insufficiency.7-12,15-22 According to several studies, 40 to 100% of U.S. and European elderly men and women still living in the community (not in nursing homes) are deficient in vitamin D.7-12,15-22 More than 50% of postmenopausal women taking medication for osteoporosis had suboptimal levels of 25-hydroxyvitamin D . below 30 ng per milliliter (75 nmol per liter).12,22
Children and young adults are also potentially at high risk for vitamin D deficiency. For example, 52% of Hispanic and black adolescents in a study in Boston23 and 48% of white preadolescent girls in a study in Maine24 had 25-hydroxyvitamin D levels below 20 ng per milliliter. In other studies, at the end of the winter, 42% of 15- to 49-year-old black girls and women throughout the United States had 25-hydroxyvitamin D levels below 20 ng per milliliter,25 and 32% of healthy students, physicians, and residents at a Boston hospital were found to be vitamin D.deficient, despite drinking a glass of milk and taking a multivitamin daily and eating salmon at least once a week.26
In Europe, where very few foods are fortified with vitamin D, children and adults would appear to be at especially high risk.1,7,11,16-22 People living near the equator who are exposed to sunlight without sun protection have robust levels of 25-hydroxyvitamin D . above 30 ng per milliliter.27,28 However, even in the sunniest areas, vitamin D deficiency is common when most of the skin is shielded from the sun. In studies in Saudi Arabia, the United Arab Emirates, Australia, Turkey, India, and Lebanon, 30 to 50% of children and adults had 25-hydroxyvitamin D levels under 20 ng per milliliter. 29-32 Also at risk were pregnant and lactating women who were thought to be immune to vitamin D deficiency since they took a daily prenatal multivitamin containing 400 IU of vitamin D (70% took a prenatal vitamin, 90% ate fish, and 93% drank approximately 2.3 glasses of milk per day)33.35; 73% of the women and 80% of their infants were vitamin D.deficient (25-hydroxyvitamin D level, <20 ng per milliliter) at the time of birth.34
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