Vitamin D, also known as calciferol, is a fat-soluble vitamin essential for maintaining several key physiological functions in the body¹². Here's a detailed overview:

Functions

1. Bone Health: Vitamin D promotes calcium absorption in the gut, which is crucial for maintaining adequate serum calcium and phosphate levels to enable normal bone mineralization and prevent hypocalcemia (low calcium levels)¹.
2. Immune System Support: It helps modulate immune functions, aiding the body in fighting off infections and reducing inflammation¹.
3. Neuromuscular Function: This vitamin is vital for muscle function, as it helps maintain proper muscle strength and coordination².
4. Other Roles: Vitamin D also modulates cell growth, differentiation, and apoptosis (programmed cell death), playing a role in reducing the risk of certain diseases¹.

Sources

1. Sunlight: The primary natural source is through the synthesis in the skin upon exposure to ultra-violet B (UVB) rays from sunlight².
2. Food: Few foods naturally contain vitamin D. These include fatty fish (like salmon, tuna, and mackerel), fish liver oils, and small amounts in beef liver, cheese, and egg yolks. In many countries, foods such as milk, orange juice, and cereals are fortified with vitamin D²³.
3. Supplements: Vitamin D is available in two forms within supplements – Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol), both of which are effective in raising vitamin D levels in the blood, although D3 might be more effective²⁴.

Recommended Intake

• The recommended dietary allowance (RDA) for vitamin D varies by age, sex, and life stage. For most adults aged 19-70, the RDA is 600 IU (15 mcg) per day, and for adults over 70 years, it is 800 IU (20 mcg) per day².
• Some experts suggest higher intakes, especially in cases of deficiency or for optimal health².

Deficiency and Health Risks

• Deficiency: Insufficient levels of vitamin D can lead to bone diseases such as rickets in children and osteomalacia in adults. It can also contribute to osteoporosis, characterized by weak and brittle bones¹².
• Risk Factors: Limited sun exposure, darker skin tones which reduce the synthesis of vitamin D, certain medical conditions that impair absorption, and aging can increase the risk of vitamin D deficiency⁴.

Safety

• The Tolerable Upper Intake Level (UL) for vitamin D is set at 4,000 IU (100 mcg) per day for adults². Excessive intake can lead to toxicity, resulting in hypercalcemia (high levels of calcium in the blood) which can cause various health issues⁴.

Vitamin D is thus essential for maintaining a range of bodily functions, and adequate levels can be ensured through a combination of sunlight exposure, diet, and supplementation when necessary.

Footnotes

1. Harvard Nutrition Source ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Office of Dietary Supplements - NIH ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

3. NHS Vitamin D ↩

4. MedlinePlus ↩ ↩² ↩³