Vitamin D Loves the Spotlight (and the Sunlight)

/ General Med-Peds, Endocrinology, Med-Peds Forum / By

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: 

  1. What is vitamin D and why do we need it?
  2. RDA and recommended sun exposure
  3. Screening recommendations
  4. 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:

Source: UpToDate

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. 

RDA

  • 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!

Screening recommendations!

AAP recommends against routine screening for vitamin D deficiency, including patients who have overweight or obesity.

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

  • Obesity
  • 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

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