Vitamin D: A Guide for Pharmacists

Vitamin D deficiency has become a growing problem in the United States. Vitamin D is a fat-soluble vitamin that is naturally present in very few foods. Patients are likely inquiring about screening for vitamin D deficiency, the best supplements to take, and health benefits of vitamin D. This guide will provide drug information and vitamin D counseling points for patients.

What is the pharmacology behind vitamin D?

Vitamin D promotes calcium absorption to assist with bone growth and remodeling. It is produced when ultraviolet rays from the sunlight strike the skin and trigger vitamin D synthesis. Vitamin D must undergo 2 chemical processes in the body after being obtained through sunlight, food, and supplements to become activated. The liver converts vitamin D to 25-hydroxyvitamin D [25(OH)D], which is also known as calcidiol.¹ The second process occurs in the kidney creating the active form 1,25-dihydroxyvitamin D [1,25(OH)₂D], which is known as calcitriol.¹

What are the benefits of vitamin D?

Low levels of vitamin D have been reported to increase the risk of fractures, cancer, diabetes, cardiovascular disease, depression, and death. However, a recent study questioned the use of vitamin D to prevent fractures. This meta-analysis examined 33 randomized clinical trials including 51145 study participants.² The study concluded that the routine use of supplements containing calcium, vitamin D, or both is not supported in community-dwelling older adults.² Meta-analyses have disadvantages as they evaluate many studies that can have differences, which may lead to biased results. However, vitamin D for fracture prevention should be further evaluated.

What levels are associated with vitamin D deficiency?

Vitamin D deficiency is generally classified as serum 25-hydroxyvitamin D [25(OH)D] concentrations of less than 30 ng/mL.³ There is limited available evidence regarding the optimal level of vitamin D, but some studies suggest about 50 ng/ml. There is mixed evidence regarding what populations should be tested for vitamin D deficiency, as laboratory testing is not always standardized.³ Groups at risk of vitamin D deficiency include the following: breastfed infants; older adults; individuals with limited sun exposure; patients with dark skin; individuals with inflammatory bowel disease and other conditions causing fat malabsorption; and patients who are obese or have undergone gastric bypass surgery.¹ Prolonged exposure to the sun without sunscreen can increase the risk of skin cancer. Therefore, it is generally not practical to obtain adequate vitamin D levels from sun exposure. Patients may need long term treatment for vitamin D deficiency and doses can vary depending on the level. The most benefit may be received from using the active form vitamin D3.

What foods contain vitamin D?

It is more difficult to obtain vitamin D than calcium from the diet. However, the flesh of fatty fish (e.g salmon, tuna, and mackerel) and fish liver oils are the best vitamin D sources. Small amounts of vitamin D are also found in beef liver, cheese, and egg yolks.

What are the recommended vitamin D intakes by age?

The American Academy of Pediatrics recommends that infants who are exclusively or partially breastfed receive a supplement with vitamin D 400 International units.⁴ Infants consuming at least 32 ounces of formula per day do not need a supplement as they are receiving adequate vitamin D from the formula.⁴ The National Osteoporosis Foundation recommends that women and men under 50 years of age receive 400-800 International units daily.⁵ Individuals 50 years of age and older should receive 800-1000 International units daily.⁵

Which OTC products should be recommended?

There are a variety of vitamin D products on the market, and pharmacists should recommend those containing the active form vitamin D3. Many Nature Made vitamin D products are verified by the United States Pharmacopeia (USP). These products will have the USP verified mark on the bottle, which means they have been tested for certain quality standards. Some patients may need higher doses for treating vitamin D deficiency, and Nature Made contains products with 5,000 International units of vitamin D.

References:

• National Institutes of Health. Vitamin D. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed March 17, 2018.
• Zhao JG, Zeng XT, Wang J, et al. Association between calcium or vitamin D supplementation and fracture incidence in community-dwelling older adults. JAMA. 2017; 318(24):2466-2482.
• U.S. Preventive Services Task Force. Vitamin D deficiency screening. https://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/vitamin-d-deficiency-screening. Accessed March 19, 2018.
• American Academy of Pediatrics. Vitamin D and iron supplements for babies: AAP recommendations. https://www.healthychildren.org/English/ages-stages/baby/feeding-nutrition/Pages/Vitamin-Iron-Supplements.aspx. Accessed March 19, 2018.
• National Osteoporosis Foundation. Calcium/vitamin D. https://www.nof.org/patients/treatment/calciumvitamin-d/. Accessed March 19, 2018.