Vitamin D always seems to be in the news (and usually about something controversial), so let’s keep it simple by tackling a few key topics:
- What is vitamin D and why do we need it?
- RDA and recommended sun exposure
- Screening recommendations
- Supplementation guidelines
What is vitamin D and why do we need it?
In short, it’s all about bone health! We need vitamin D to absorb calcium.
Children gain the most bone mass during adolescence (40-60%) with peak bone mass accumulation at age 12.5yo for girls and 14yo for boys.
- Interestingly, bone mass slightly lags linear growth. Some people think this is why early adolescents are at increased risk for some types of fractures!
Many other theorized benefits, but not well-demonstrated.
- Vitamin D supplementation was previously thought to have a role in fall prevention in the elderly, but recent evidence argues against this.
Sources of vitamin D
Vitamin D3 (cholecalciferol) is synthesized in the skin thanks to UV light from sun exposure.
- Sun exposure on face/arms for 5-15 minutes 2-3x weekly is equivalent 3000 IU
D3 and D2 (ergocalciferol) can also be found in a few foods, including cod liver oil, fatty fish, fortified foods (milk, juice, infant formula)
D3 and D2 are converted to 25-OH-D (calcidiol) in the liver, then to 1,25-OH-D (calcitriol) in the kidneys:
Calcitriol is the active form of vitamin D. Its half-life is ~4 hours (compared with 2-3 weeks for calcidiol). Calcitriol has several key functions:
- promotes intestinal absorption of calcium and phosphorus
- increases renal reabsorption of filtered calcium
- increases bone resorption
Clinical pearl: High sodium diet promotes renal calcium excretion (proximal tubule)
Clinical pearl: Patients without parathyroid function (e.g., s/p parathyroidectomy) lack PTH, thus there is no stimulus for the kidneys to activate vitamin D or to reabsorb calcium. These patients need calcitriol and calcium supplementation.
- Clinical pearl: In infants, 32 oz/day of standard formula contains 400 IU of vitamin D.
- The AAP recommends that all infants and children have a minimum intake of 400 IU of vitamin D per day beginning soon after birth. This means that exclusively breastfed infants as well as infants taking <32 oz/day of standard formula should receive vitamin D supplementation!
AAP recommends against routine screening for vitamin D deficiency, including patients who have overweight or obesity.
- AAP’s report on Optimizing Bone Health in Children and Adolescents advises screening for vitamin D deficiency only in patients with disorders associated with low bone mass such as rickets and/or a history of recurrent, low-trauma fractures.
USPSTF gives “I” grade to routine vitamin D screening for the general population (i.e., the current evidence is insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency in asymptomatic adults.)
American Society for Clinical Pathology specifically recommends against general population screening for vitamin D deficiency.
The Endocrine Society recommends screening patients “at risk”, which includes
- Fat malabsorption (includes bariatric surgery)
- Nephrotic syndrome (urinary loss of vitamin D-binding protein)
- Primary hyperparathyroidism
- Low sun exposure / wearing sunscreen
- Darker skin at higher latitudes in northern hemisphere (and lower latitudes in southern hemisphere)
- Use of anticonvulsants or ART (both enhance vitamin D catabolism)
Treatment for vitamin D deficiency
Typical treatment threshold is <20 ng/mL.
- Remember that vitamin D insufficiency is 20-30 ng/mL—evidence is inconsistent on need to treat patients falling into this category
For patients of all ages with VDD, it’s reasonable to start with 6 weeks of 50,000 IU of D2/D3 supplementation once weekly.
- For patients older than toddlers, it is reasonable to continue this initial dose up to 8 weeks
Following initial supplementation, we should start maintenance therapy of 400 IU in infants/toddlers and 600-1000 IU in older kids and adults.
- May repeat course of treatment
Blog post based on Med-Peds Forum talk by Julia Solomon, PGY2