Description

• Vitamins are essential micronutrients required for normal metabolism, growth, and development.
• Vitamin supplementation in food products, adequate food security, and availability of supplements make vitamin deficiencies less common in developed countries. Certain populations are at increased risk.
• Toxicity is rare for water-soluble vitamins, whereas possible with fat-soluble vitamins (A, D, E, K).

Epidemiology

Incidence

• Higher incidence seen in geriatric patients, pregnant women, exclusively breastfed infants, individuals with highly restricted diets or certain chronic disease states
• Increased risk among individuals from Africa and Southeast Asia
• True incidence is unknown because most vitamin deficiencies are asymptomatic.

Prevalence

• Varies by age groups, comorbid conditions, geography, and setting (i.e., urban, rural)
• The prevalence of vitamin B₁₂ deficiency is ~6% in patients <60 years old and increases to ~20% after age 60 (1).
• Vitamin D deficiency prevalence is increased in individuals with darker skin pigmentation, obesity, low dietary intake of vitamin D, or low sunlight exposure. This deficiency is seen in ~5% of the general population, with non-Hispanic blacks having the highest prevalence.

Etiology and Pathophysiology

• Deficiency usually develops from one of five mechanisms: reduced intake, diminished absorption, increased use, increased demand, or increased excretion
• Chronic disease states: HIV, malabsorption (i.e., celiac sprue, short bowel syndrome), chronic liver and kidney disease, alcoholism, malignancies, pernicious anemia, inborn errors of metabolism
• Bariatric surgeries: gastric bypass, gastrectomy, small or large bowel resection
• Related to certain drugs: prednisone, phenytoin, isoniazid, protease inhibitors, methotrexate, phenobarbital, alcohol, nitrous oxide, H₂ receptor antagonists, metformin, colchicine, cholestyramine, 5-fluorouracil, 6-mercaptopurine, azathioprine, chloramphenicol, proton pump inhibitors, chronically used antibiotics, penicillamine, hydralazine
• Malnutrition, imbalanced nutrition, obesity, fad diets, extreme vegetarianism, total parenteral nutrition, bulimia/anorexia, other eating disorders, parasitic infection

Genetics

• Cystic fibrosis
• Hartnup disease, A-β-lipoproteinemia
• Rare genetic predisposition
  • Autoimmune disease (i.e., pernicious anemia)
  • Congenital enzyme deficiencies (i.e., biotinidase or holocarboxylase synthetase deficiency)
  • Transcobalamin II deficiency
  • Ataxia with vitamin E deficiency (AVED)

Risk Factors

Poverty, malnutrition, chronic excessive alcohol intake, chronic disease states, advanced age, dietary restrictions, bariatric surgery, certain medications, and exclusively breastfed infants

General Prevention

• Ingesting large and varied amounts of vitamin supplements increases risk of toxicity and drug–drug interactions and is not recommended.
• Antioxidant supplements have not been shown to impact cancer incidence; increased mortality risk seen in some studies (2)
• Avoid restrictive diets.
• USPSTF recommends against low-dose supplementation with vitamin D (<400 IU) and calcium (<1,000 mg) to reduce fracture risk in community-dwelling postmenopausal women (3).
• USPSTF concludes insufficient evidence of benefits and harms of daily supplementation with doses >400 IU of vitamin D and >1,000 mg of calcium for primary prevention of fractures in community-dwelling, postmenopausal women (3).
• USPSTF also concludes that current evidence is insufficient to assess the balance of the benefits and harms of vitamin D and calcium supplementation, for primary prevention of fractures in men and premenopausal women (3).
• USPSTF recommends all women planning or capable of pregnancy take a daily supplement containing 0.4 to 0.8 mg of folic acid (4)[A].
• USPSTF recommends against using β-carotene or vitamin E supplements for the prevention of cardiovascular disease or cancer (2).
• All infants should receive 400 IU/day of vitamin D soon after birth if exclusively or partially breastfed (5).

Commonly Associated Conditions

Anemia, neuropathies, dermatitis, visual disturbances