How can I get enough vitamin D?

How to Get Adequate Vitamin D

The most effective way to ensure adequate vitamin D levels is through a combination of sensible sun exposure, dietary sources, and supplementation with 800 IU daily for most adults, increasing to 2,000 IU daily for high-risk individuals. 1

Sources of Vitamin D

Sun Exposure

• Vitamin D is naturally produced in the skin through UVB radiation exposure
• Humans are largely dependent on UVB-radiation-induced photosynthesis of vitamin D 2
• Sensible sun exposure is an inexpensive and enjoyable way to maintain vitamin D stores for those not at risk of deficiency 3
• However, excessive sun exposure should be avoided due to skin cancer risk

Dietary Sources

• Few foods naturally contain vitamin D, making it difficult to obtain adequate amounts from diet alone 2
• Natural food sources include:
  • Fatty fish (salmon, mackerel)
  • Egg yolks
  • Fortified foods (milk, orange juice, cereals)

Supplementation

Supplementation is recommended for:

1. High-risk populations without baseline measurement 4, 1:

   • Dark-skinned or veiled individuals: 800 IU/day
   • Adults ≥65 years: 800 IU/day
   • Institutionalized individuals: 800 IU/day

2. Other individuals after 25(OH)D measurement if levels <30 ng/mL 4, 1:

   • Initial corrective dose: 50,000 IU weekly for 8 weeks
   • Followed by maintenance dose: 800 IU/day

Optimal Dosing Recommendations

Daily Maintenance Dosing

• General adult population: 600-800 IU/day 1
• Adults over 70 years: 800 IU/day 1
• High-risk individuals: 800-2,000 IU/day 1, 5

Correcting Deficiency

• For documented vitamin D deficiency (<20 ng/mL):
  • 50,000 IU weekly for 8 weeks 1
  • Followed by appropriate maintenance dose
  • Recheck levels after 3 months of supplementation

Dosing Considerations

• Rule of thumb: 1,000 IU daily increases 25(OH)D by approximately 10 ng/mL 4
• Vitamin D3 (cholecalciferol) is preferred over vitamin D2 (ergocalciferol) for long-term supplementation 4, 1
• Daily dosing is physiologic, but weekly or monthly dosing can be similarly effective 4
• Avoid single large annual doses (e.g., 500,000 IU) due to potential adverse effects 4

Special Populations

• Obesity: May require higher doses due to sequestration in adipose tissue 1
• Malabsorption syndromes: May require higher doses and more frequent monitoring 4, 1
• Chronic kidney disease: Requires specialized approaches 1
• Patients taking medications affecting vitamin D metabolism: May need dose adjustments 1

Target Levels and Monitoring

• Optimal vitamin D level: >30 ng/mL (75 nmol/L) 1
• Deficiency: <20 ng/mL (50 nmol/L) 1
• Insufficiency: 20-30 ng/mL (50-75 nmol/L) 1
• Safety range: 30-80 ng/mL 4

Safety Considerations

• Safe upper limit for daily intake: 4,000 IU for most adults 1
• Vitamin D toxicity typically occurs at levels above 150 ng/mL 1
• Monitor calcium and phosphorus levels when supplementing at higher doses 1
• Discontinue therapy if corrected total calcium exceeds 10.2 mg/dL 1

Common Pitfalls

• Underdosing: Many standard multivitamins contain only 400 IU, which may be insufficient for high-risk individuals
• Inconsistent supplementation: Intermittent use may not maintain adequate levels
• Overreliance on diet alone: Most diets provide insufficient vitamin D
• Seasonal variations: Vitamin D production from sunlight varies by season, latitude, and skin pigmentation
• Failure to recognize high-risk groups: Certain populations need higher supplementation doses

Recent research suggests that 2,000 IU/day may be more effective than lower doses for maintaining optimal vitamin D levels, especially during winter months 5, but this should be balanced against current guidelines recommending 800 IU/day for most adults 1.