Vitamin D
Personalized vitamin D dosing, guided by regular blood monitoring, significantly reduced recurrent heart attacks by 52% in a recent trial.
About Vitamin D
Vitamin D is a fat-soluble vitamin and conditionally essential hormone vital for bone health, muscle function, and immune system support. It helps the body absorb calcium and phosphorus, minerals necessary for strong bones and teeth.
Key Functions
- Bone Health: Vitamin D's primary role is maintaining calcium and phosphorus levels in the blood, which prevents bone disorders like rickets in children and osteomalacia (softening of the bones) and osteoporosis (weakening of the bones) in adults.
- Muscle Function: It supports muscle strength, which can help reduce the risk of falls, especially in older adults.
- Immune System: The immune system requires vitamin D to fight off invading bacteria and viruses.
- Other Roles: Research suggests potential links to reduced risks of certain cancers, heart disease, autoimmune disorders, and type 2 diabetes, although more research is needed to confirm these non-skeletal benefits.
Sources of Vitamin D
| Source |
Details |
| Sunlight |
The skin produces vitamin D3 when directly exposed to ultraviolet B (UVB) rays from the sun. It is a major natural source, but factors like latitude, season, time of day, skin color, and sunscreen use can limit production. Health experts recommend limiting sun exposure without protection due to skin cancer risk. |
| Food |
Very few foods naturally contain significant amounts of vitamin D. Good natural sources include fatty fish (salmon, tuna, mackerel, sardines), fish liver oils, beef liver, cheese, and egg yolks. |
| Fortified Foods |
Many common foods have vitamin D added to them (fortified), such as milk, many breakfast cereals, and some brands of orange juice, yogurt, and plant-based milks. |
| Supplements |
Vitamin D is available in two forms in supplements: D2 (ergocalciferol, from plants) and D3 (cholecalciferol, from animals/lichen). Both effectively raise blood levels, but D3 might raise them higher and for longer. |
Recommended Intake and Deficiency
The daily recommended amount of vitamin D varies by age. For most adults (ages 19-70), the recommendation is 600 IU (International Units), increasing to 800 IU for adults over 70.
Deficiency is a common global issue and often asymptomatic in its early stages. Risk factors include limited sun exposure, dark skin, older age, obesity, and conditions affecting fat absorption (e.g., celiac disease, Crohn's disease). A blood test (measuring 25-hydroxyvitamin D levels) can diagnose a deficiency.
Risks of Excessive Intake
Vitamin D toxicity (hypervitaminosis D) is rare and almost always occurs from overusing supplements, not from sun exposure. Symptoms are mainly due to a buildup of calcium in the blood (hypercalcemia) and can include nausea, vomiting, weakness, confusion, and kidney damage. The safe upper limit for adults is 4,000 IU per day, though higher doses may be prescribed by a healthcare professional to treat a diagnosed deficiency.
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