Vitamin D is a fat-soluble vitamin that functions as a hormone in the human body. It plays critical roles in various bodily functions, including:

1. Bone Health: Vitamin D promotes calcium absorption and helps maintain adequate blood levels of calcium and phosphorus, which are necessary for healthy bones and teeth¹². Deficiency in children can cause rickets, while in adults it can lead to osteomalacia and osteoporosis².

2. Immune Function: It supports the immune system by promoting pathogen-fighting effects of monocytes and macrophages—white blood cells that are crucial to immune defense³.

3. Muscle Function: Vitamin D is important for muscle function, helping prevent falls and fractures in the elderly³.

4. Brain Health: It has roles in brain health, potentially reducing the risk of cognitive decline and neurodegenerative diseases².

Sources of Vitamin D

• Sunlight: The skin synthesizes vitamin D when exposed to UV-B radiation from the sun. This is the primary natural source of vitamin D⁴.
• Diet: Few foods naturally contain vitamin D. These include fatty fish (such as salmon, mackerel, and sardines), cod liver oil, egg yolks, and cheese. Some foods are fortified with vitamin D, such as milk, cereals, and orange juice⁴.
• Supplements: There are two forms of vitamin D supplements: D2 (ergocalciferol) and D3 (cholecalciferol). Both can help maintain adequate levels in the body³.

Recommended Intake

• The Recommended Dietary Allowance (RDA) for adults 19 years and older is 600 IU (15 mcg) per day. For adults over 70 years, the RDA is 800 IU (20 mcg) per day³.
• The Tolerable Upper Intake Level (UL) for adults is 4,000 IU (100 mcg) per day³.

Deficiency and Risks

Vitamin D deficiency is linked to a host of health issues, including:

• Bone Disorders: Rickets in children and osteomalacia or osteoporosis in adults².
• Chronic Illnesses: There is some evidence suggesting low vitamin D levels are associated with conditions like cardiovascular disease, diabetes, and certain cancers. However, an association does not mean causation¹.

Risk Groups

• Limited Sun Exposure: Individuals in regions with limited sunlight or who have lifestyles that limit sun exposure may be at risk.
• Darker Skin: Higher melanin levels can reduce the skin's ability to produce vitamin D from sunlight⁴.
• Elderly: Aging can reduce the skin's ability to synthesize vitamin D⁴.

Conclusion

Vitamin D is crucial for overall health, particularly for bone and immune health. While sun exposure and dietary intake are important sources, supplementation may be necessary for those at risk of deficiency⁴.

Footnotes

1. "Mayo Clinic Q and A: How much vitamin D do I need?" Mayo Clinic. ↩ ↩²

2. "Vitamin D: Benefits, deficiency, sources, and dosage," Medical News Today. ↩ ↩² ↩³ ↩⁴

3. "Vitamin D," Harvard T.H. Chan School of Public Health. ↩ ↩² ↩³ ↩⁴ ↩⁵

4. "Office of Dietary Supplements - Vitamin D," NIH. ↩ ↩² ↩³ ↩⁴ ↩⁵