What is the recommended oral supplementation regimen for vitamin D and ferritin in a general adult population, including pregnant women and geriatric individuals?

Optimal Oral Supplementation of Vitamin D and Iron

Vitamin D Supplementation

For general adults, take 2000 IU of vitamin D3 (cholecalciferol) daily with a fat-containing meal to achieve and maintain optimal serum 25(OH)D levels above 30 ng/mL. 1, 2

Standard Dosing by Population

General adult population (ages 19-70):

• Minimum baseline: 600-800 IU daily meets needs of 97.5% of the population 3, 4
• Optimal preventive dose: 2000 IU daily maintains levels >30 ng/mL in >90% of adults and is safe for long-term use 1, 2
• High-risk populations (dark skin, obesity, limited sun exposure, vegetarians): 1500-4000 IU daily 3, 5

Adults over 70 years:

• Minimum: 800 IU daily 3
• Optimal for fall/fracture prevention: 800-1000 IU daily 6

Pregnant women:

• Standard dose: 1000-2000 IU daily (>40 mcg) 7, 5
• High-risk pregnant women (dark skin, obesity, post-bariatric surgery): 4000 IU daily is safe and most effective 5
• Preconception: Start 2000-4000 IU daily before conception if high-risk 5

Formulation Selection

Vitamin D3 (cholecalciferol) is strongly preferred over D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly with intermittent dosing 6, 3

Administration Timing

Take vitamin D with the largest, fattiest meal of the day to maximize absorption, as it is a fat-soluble vitamin requiring dietary fat for optimal intestinal uptake 6, 5

Treatment of Deficiency (25(OH)D <20 ng/mL)

Loading phase:

• Standard regimen: 50,000 IU weekly for 8-12 weeks 7, 6
• Severe deficiency (<10 ng/mL): 50,000 IU weekly for 12 weeks 6

Maintenance after loading:

• Standard: 2000 IU daily or 50,000 IU monthly 6
• Post-bariatric surgery or malabsorption: Consider 2000-4000 IU daily or intramuscular administration if oral fails 6, 8

Monitoring Protocol

Recheck 25(OH)D levels 3 months after starting supplementation to assess response and adjust dosing, as vitamin D has a long half-life requiring adequate time to reach steady-state 6, 3

Target Levels

Optimal range: 30-80 ng/mL for health benefits including fracture prevention 6, 3 Upper safety limit: 100 ng/mL 6, 3

Critical Pitfalls to Avoid

• Never use single mega-doses (>300,000 IU) as they may increase falls and fractures 6, 3
• Do not use active vitamin D analogs (calcitriol, alfacalcidol) to treat nutritional deficiency 6
• Ensure adequate calcium intake (1000-1500 mg daily) as vitamin D enhances calcium absorption and adequate calcium is necessary for clinical response 6, 5

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Iron (Ferritin) Supplementation

For iron deficiency, take 45-60 mg of elemental iron daily on an empty stomach (or with vitamin C if tolerated), separated from calcium supplements by at least 2 hours. 7

Standard Dosing by Population

General adults with iron deficiency:

• Standard dose: 45-60 mg elemental iron daily 7
• Treatment of documented deficiency: 150-200 mg elemental iron daily 7

Pregnant women:

• Minimum: 45 mg elemental iron daily 7
• Standard pregnancy dose: 45-60 mg elemental iron daily 7
• Post-bariatric surgery pregnancy: 45-60 mg elemental iron daily (>18 mg for adjustable gastric banding) 7

Women of childbearing age or at risk of anemia:

• Preventive dose: 50-100 mg elemental iron daily 7

Formulation Selection

Ferrous sulfate is the standard formulation providing elemental iron 9

• Adult serving: 1 tablet two to three times daily 9
• Do not crush or chew tablets 9

Administration Timing and Optimization

Take iron on an empty stomach (1 hour before or 2 hours after meals) for maximum absorption, though taking with food reduces gastrointestinal side effects if needed 7

Separate iron from calcium supplements by at least 2 hours as calcium interferes with iron absorption 7

Take iron with vitamin C (orange juice or vitamin C supplement) to enhance absorption if gastrointestinal tolerance allows 7

Monitoring Protocol

Check ferritin, iron studies (including transferrin saturation), and complete blood count:

• During pregnancy: At least once per trimester 7
• Post-bariatric surgery: Every 3-6 months initially, then annually once stable 7
• General population: 3 months after starting supplementation, then as clinically indicated

Increase dose as needed to maintain ferritin within normal limits 7

Target Levels

Maintain ferritin within normal limits (typically 30-200 ng/mL for women, 30-300 ng/mL for men, though pregnancy-specific ranges apply) 7

Critical Pitfalls to Avoid

• Do not take iron with calcium-containing supplements, antacids, or dairy products as these significantly reduce absorption 7
• Do not take iron with tea or coffee as tannins inhibit absorption
• Monitor for constipation (most common side effect) and adjust formulation or add stool softener if needed
• In pregnant women post-bariatric surgery, check iron studies each trimester as this population has higher risk of deficiency 7
• Consider intramuscular iron if oral supplementation fails to achieve target ferritin levels, particularly in malabsorption syndromes 7

Special Considerations for High-Risk Populations

Post-bariatric surgery patients:

• Require minimum 45 mg elemental iron daily (>18 mg for adjustable gastric banding) 7
• May need higher doses (150-200 mg daily) if deficiency develops 7
• Consider intramuscular iron if oral fails to maintain adequate levels 7

Pregnant women with obesity or post-bariatric surgery:

• Monitor ferritin, iron studies, and complete blood count at least once per trimester 7
• Maintain minimum 45-60 mg elemental iron daily throughout pregnancy 7