Vitamin supplementation in healthy patients: What does the evidence support?

Vitamin D

Vitamers: Cholecalciferol (D3); ergocalciferol (D2)

Physiologic role: Hydroxylation in liver and kidney required to activate. Promotes dietary calcium absorption, enables normal bone mineralization. Also involved in modulation of cell growth, and neuromuscular and immune function

Dietary sources: Few natural dietary sources, which include fatty fish, fish liver oils; small amount in beef liver, cheese, egg yolks. Primary sources include fortified milk and endogenous synthesis in skin with UV exposure

Calciferol is a fat-soluble vitamin required for calcium and bone homeostasis. It is not naturally available in many foods but is primarily produced endogenously in the skin with ultraviolet light exposure.²

The AAP recommends supplementing exclusively breastfed infants with 400 IU/d of vitamin D to prevent rickets.

Bone density and fracture risk reduction are the most often cited benefits of vitamin D supplementation, but this has not been demonstrated consistently in RCTs. Multiple systematic reviews showing inconsistent benefit of vitamin D (with or without calcium) on fracture risk led the USPSTF to conclude that there is insufficient evidence (grade I) to issue a recommendation on vitamin D and calcium supplementation for primary prevention of fractures in postmenopausal women.^49-51 Despite some initial evidence suggesting a benefit of vitamin D supplementation on falls reduction, 3 recent systematic reviews did not demonstrate this in community-dwelling elders,^54-56 although a separate Cochrane review did suggest a reduction in rate of falls among institutionalized elders.⁵⁷

The takeaway: Given these findings, the USPSTF has recommended against (grade D) vitamin D supplementation to prevent falls in community-dwelling elders.⁵⁵

Beyond falls. While the vitamin D receptor is expressed throughout the body and observational studies have suggested a correlation between vitamin D status and many outcomes, extensive RCT data has generally failed to demonstrate extraskeletal benefits from supplementation. Meta-analysis data have demonstrated potential reductions in acute respiratory infection rates and asthma exacerbations with vitamin D supplementation. There is also limited evidence suggesting a reduction in preeclampsia and low-birthweight infant risk with vitamin D supplementation in pregnancy. However, several large meta-analyses and systematic reviews have investigated vitamin D supplementation’s effect on all-cause mortality and found no consistent data to support an association.^41,58-62

Multiple systematic reviews have investigated and found high-quality evidence demonstrating no association between vitamin D supplementation and cancer^41,63-66,121 or cardiovascular disease risk.^41,70,71 There is high-quality data showing no benefit of vitamin D supplementation for multiple additional diseases, including diabetes, cognitive decline, depression, pain, obesity, and liver disease.^{43,72-75,85-90,122}

The takeaway: Due to poor availability in breastmilk, the American Academy of Pediatrics (AAP) recommends supplementing exclusively breastfed infants with 400 IU/d of vitamin D to prevent rickets.¹²³ RCT data support high-dose supplementation of lactating women (6400 IU/d) as an alternative strategy to supplementation of the infant.¹²⁴ The AAP recommends that all nonbreastfeeding infants and older children ingesting < 1000 mL/d of vitamin D–fortified formula or milk should also be supplemented with 400 IU/d of vitamin D.¹²³ Despite these universal recommendations for supplementation, evidence is mixed on the effect of vitamin D supplementation on bone health in children.^52,53

Although concerns about vitamin D supplementation and increased risk of urolithiasis and hypercalcemia have been raised,^51,62,121 systematic reviews have not demonstrated significant, clinically relevant risks, even with high-dose supplementation (> 2800 IU/d).^125,126

Vitamin K

Vitamers: Phylloquinone (K1); menaquinones (K2)

Physiologic role: Coenzyme for synthesis of proteins involved in hemostasis and bone metabolism

Dietary sources: Phylloquinone is found in green leafy vegetables, vegetable oils, some fruits, meat, dairy, and eggs. Menaquinone is produced by gut bacteria and present in fermented foods

Vitamin K includes 2 groups of similar compounds: phylloquinone and menaquinones. Unlike other fat-soluble vitamins, vitamin K is rapidly metabolized and has low tissue storage.²

Children taking multivitamins were often found to have excess levels of potentially harmful nutrients, such as retinol, zinc, and folic acid.

Administration of vitamin K 0.5 to 1 mg intramuscularly (IM) to newborns is standard of care for the prevention of vitamin K deficiency bleeding (VKDB). This is supported by RCT data demonstrating a reduction in classic VKDB (occurring within 7 days)⁹¹ and epidemiologic data from various countries showing a reduction in late-onset VKDB with vitamin K prophylaxis programs.¹²⁷ Oral dosing appears to reduce the risk of VKDB in the setting of parental refusal but is less effective than IM dosing.^128,129

Vitamin K’s effects on bone density and fracture risk have also been investigated. Systematic reviews have demonstrated a reduction in fracture risk with vitamin K supplementation,^92,93 and European and Asian regulatory bodies have recognized a potential benefit on bone health.² The FDA considers the evidence insufficient at this time to support such a claim.² Higher dietary vitamin K consumption has been associated with lower risk of cardiovascular disease in observational studies⁹⁴ and supplementation was associated with improved disease measures,¹³⁰ but no patient-oriented outcomes have been demonstrated.¹³¹

The takeaway: The administration of vitamin K 0.5 to 1 mg intramuscularly (IM) to newborns is standard of care for the prevention of VKDB. Vitamin K may lead to a reduction in fracture risk, but the FDA considers the evidence insufficient. Vitamin K’s potential link to a lowered risk of cardiovascular disease has not been demonstrated with patient-­oriented outcomes. Vitamin K has low potential for toxicity, although its interaction with vitamin K antagonists (ie, warfarin) is clinically relevant.

Continue to: MULTIVITAMINS