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Vitamin D (Cholecalciferol): The Sunshine Nutrient for Bone Health

Vitamin D₃ (cholecalciferol) is the form synthesized in skin upon UVB exposure and found in animal foods/supplements. It’s essential for calcium absorption and bone mineralization.

Sources

Sunlight: 10–30 min midday sun (arms/legs) 2–3×/wk (varies by latitude, skin tone, age, sunscreen).
Food: Fatty fish (salmon, mackerel, sardines), egg yolks, UV-exposed mushrooms (D₂), fortified milk, OJ, cereals.
Supplements: D₃ preferred (more potent/longer half-life than D₂).

Deficiency Consequences

Children: Rickets — bowed legs, delayed growth, bone pain, muscle weakness.
Adults: Osteomalacia (bone pain, proximal weakness, pseudofractures), osteoporosis, falls.
Extra-skeletal: Immune dysregulation, depression, cardiovascular risk, autoimmune links.

Testing & Targets

Serum 25(OH)D: <12 ng/mL = deficient; 12–20 = insufficient; 20–50 = adequate; >50 = excess risk.
Endocrine Society: target 30–50 ng/mL for at-risk groups.

Supplementation Guidelines (IOM/Endocrine Society)

Key Points

Fat-soluble → take with fat-containing meal.
Obesity, malabsorption, dark skin, aging, medications (steroids, anticonvulsants) increase need.
Vitamin K2 (MK-7) synergizes for bone/cardiovascular health.
Test, don’t guess. Megadoses (>10,000 IU/day long-term) risk hypercalcemia.

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Group	RDA (IU/day)	Upper Limit (IU/day)
Infants 0–12 mo	400	1,000–1,500
Children 1–18 yr	600	2,500–4,000
Adults 19–70	600	4,000
Adults >70	800	4,000
Pregnancy/Lactation	600	4,000