Vitamin D plays a crucial role in maintaining bone strength, muscle function, and immune health.
Since few foods naturally contain this nutrient, fortified products and supplements are vital for maintaining healthy levels, especially in regions with limited sunlight.
What is vitamin D?
Vitamin D is a fat-soluble nutrient that acts as a precursor to the hormone calcitriol.
It exists as D2, derived from plants and fungi, and D3, obtained from animal sources or produced in the skin through sunlight exposure.
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Once in the body, it is activated in the liver and kidneys, where it supports multiple vital functions.
Key functions in the body
Vitamin D enhances calcium and phosphorus absorption, both essential for strong bones and teeth.
It also regulates immune activity and supports muscle strength and balance, helping to reduce the risk of falls in older adults.
A global deficiency problem
Despite the body’s ability to synthesize vitamin D from sunlight, deficiency remains widespread, affecting around one billion people worldwide.
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It can lead to fatigue, muscle weakness, and bone disorders such as rickets and osteomalacia.
Top dietary sources
Animal-based foods are the richest natural sources.
One tablespoon of cod liver oil provides about 1,360 IU, while a three-ounce serving of salmon offers roughly 570 IU.
Smaller amounts are found in beef liver, egg yolks, and sardines.
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Plant and mushroom sources
Mushrooms exposed to UV light can provide up to 366 IU per half cup, while unexposed mushrooms contain negligible amounts.
Both D2 and D3 are absorbed by the body, but D3 is more effective at maintaining stable vitamin D levels.
Fortified foods
Many foods are fortified to help prevent deficiency.
In several countries, milk, plant-based alternatives, yogurt, margarine, and breakfast cereals are enriched with vitamin D and contribute significantly to overall intake.
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Vitamin D and bone health
Adequate levels of vitamin D, combined with calcium, reduce the risk of fractures in older adults.
Chronic deficiency can lead to poor bone mineralization and a higher risk of osteoporosis over time.
Role in immune function
Vitamin D plays a key role in both innate and adaptive immunity.
Studies show that moderate daily supplementation can lower the risk of respiratory infections, especially in children.
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Recommended daily intake
According to U.S. guidelines, adults aged 19–70 should consume 600 IU daily, increasing to 800 IU after age 70.
Infants require 400 IU, while pregnant and breastfeeding women are advised to take 600 IU per day.
Groups at risk of deficiency
Those most at risk include older adults, people with darker skin, individuals who are overweight, those with limited sun exposure, and people with chronic illnesses or absorption disorders.
Overdose and safety
Excessive vitamin D intake from supplements can cause elevated calcium levels, leading to nausea, weakness, and, in severe cases, kidney damage.
However, toxicity does not occur from sunlight or food sources.
A balanced approach
Maintaining healthy vitamin D levels requires a balanced combination of sunlight exposure, natural dietary sources, and fortified foods.
Supplements can be helpful but should be used responsibly and ideally under medical guidance.
This article is based on information from News-Medical.net.