Vitamin D Family
Understanding Natural Synthesis and Dietary Sources
Overview
Vitamin D is a fat-soluble micronutrient that plays central roles in calcium absorption, bone mineralization, and cellular differentiation. Unlike other vitamins, vitamin D can be synthesized by the body through sunlight exposure on skin, and it also appears in specific food sources.
Natural Synthesis Through Sunlight
When skin is exposed to ultraviolet B (UVB) radiation from sunlight, a cholesterol derivative in the skin converts to pre-vitamin D3. This substance then travels to the liver and kidneys for conversion to the active form used by the body. The efficiency of this synthesis varies with:
- Geographic latitude and season
- Time of day (midday sun provides stronger UVB)
- Skin pigmentation (darker skin requires longer exposure)
- Age (synthesis decreases with age)
- Use of sunscreen (reduces but does not eliminate synthesis)
Dietary Food Sources
Vitamin D appears naturally in limited food sources and in fortified foods:
Natural Sources
- Fatty fish (salmon, mackerel, sardines)
- Fish liver oils
- Egg yolks
- Mushrooms exposed to sunlight
- Fermented fish products
Fortified Foods
- Fortified milk and dairy alternatives
- Fortified breakfast cereals
- Fortified orange juice
- Fortified plant-based beverages
- Fortified grains and flours
General Physiological Roles
Vitamin D functions in the body include:
| Function | Description |
|---|---|
| Calcium Absorption | Enables intestinal absorption of dietary calcium |
| Bone Mineralization | Supports deposition of calcium and phosphorus into bone matrix |
| Parathyroid Function | Regulates parathyroid hormone for blood calcium balance |
| Cell Growth | Supports cell differentiation and proliferation |
| Immune Function | Contributes to immune cell function and response |
| Neuromuscular Function | Supports muscle contraction and nerve transmission |
Research Context
Vitamin D research is extensive and ongoing. International reference values for daily intake vary slightly among health organizations but generally range from 400-800 IU for children and adults, with higher recommendations for older adults. Individual needs may vary based on factors including age, skin tone, geographic location, and dietary patterns.
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