August is usually a month of abundant sunshine that provides ample opportunity to form vitamin D from sunlight exposure. Recently, patients have begun to request testing for vitamin D levels based on perceived risks for deficiency. Is vitamin D deficiency the new en vogue disorder? What does the evidence say?
Vitamin D obtained from sun exposure, food, and supplements only partially supplies the required amounts and must be converted in the body before being useful. Vitamin D is essential for proper bone health, calcium absorption, cell growth, neuromuscular and immune function, and to reduce inflammation. In children, vitamin D deficiency can lead to rickets and skeletal deformities. Adults can develop muscle weakness, osteomalacia, osteopenia, and osteoporosis. The Endocrine Society recently released a new clinical practice guideline (CPG) on the evaluation, treatment, and prevention of vitamin D deficiency.1 Recommendations include screening at-risk individuals for deficiency, measuring these patients' vitamin D levels with a reliable assay, and treating deficient patients with either vitamin D2 or D3.
Who is at risk?
The National Health Institutes Office of Dietary Supplements2 has identified the following as at-risk individuals: breast-fed infants who do not consume vitamin D fortified milk, older adults whose skin cannot synthesize vitamin D efficiently, people with limited sun exposure, people with dark skin, people with fat malabsorption (some dietary fat in the stomach is necessary for vitamin D synthesis), and people who are obese or have had gastric bypass surgery because fat sequesters vitamin D and absorption is compromised when part of the upper small intestine is removed. The effects of UV radiation exposure and vitamin D synthesis can vary depending on the season (fewer daylight hours in winter), time of day (UV rays greatest between 10 a.m. and 3 p.m.), length of day (hours of daylight versus darkness), cloud cover and smog (filters UV rays), skin melanin content (increased melanin in darker skin reduces the skin's ability to produce vitamin D), and sunscreen. Products with an SPF of 8 or higher significantly block UV rays. Unfortunately, many people do not apply sunscreen to all exposed areas of the body, do not apply enough, and do not reapply it as directed.
Tests and treatments
The most reliable indicator of vitamin D status is serum 25-hydroxyvitamin D or 25(OH)D. Levels less than 30 nmol/L (12 ng/mL) result in deficiency states; levels from 30 to 50 nmol/L (12–20 ng/mL) signal insufficiency; levels at or over 50 nmol/L (20 ng/mL or greater ) signal adequate vitamin D for bone and overall health in healthy individuals; and levels above 125 nmol/L ( over 50 ng/mL) warn of potential adverse reactions.
To treat vitamin D deficiency, CPG recommends increasing dietary intake of foods high in vitamin D, such as fatty fish, fish liver oils, beef liver, cheese, egg yolks, and fortified foods such as milk, some juices, and ready-to-eat cereals. NPs should encourage safe sun exposure and prescribe dietary supplements when indicated. Recommended daily allowance of vitamin D is 400 international units/day for infants up to 12 months, 600 units/day for ages 1 to 70 years, and 800 units/day for persons over 70 years. Check potential interactions of vitamin D supplements with medications a person is already taking.
The CPG does not recommend screening persons who are not at risk for deficiency or prescribing vitamin D as a cardio-protective agent. The Endocrine Society develops CPGs based on the scientific review of literature to determine the state of the science. To provide patients with high-quality care, we should look for the best available evidence to guide assessment/evaluation, diagnosis, and treatment. We do not have to test just because a patient requests it. Effectively communicating with patients is part of good clinical decision making.
Jamesetta Newland, PhD, RN, FNP-BC, FAANP, FNAP