Feb. 28, 2026, 6:00 a.m. ET
Even in an era filled with diverse food options and supplements, certain vitamin and mineral deficiencies are still notably prevalent. Among these, vitamin D stands out as one of the most commonly deficient nutrients. Studies indicate that a significant segment of the global population suffers from suboptimal vitamin D levels, partly due to our modern lifestyles that tend to keep many indoors, away from sunlight.
This is important because vitamin D exists in two primary forms, and vitamin D3 is the one that necessitates sunlight exposure to be synthesized in the body effectively. According to Caroline Susie, a registered dietitian and national spokesperson for the Academy of Nutrition and Dietetics, “Vitamin D is essential, along with calcium, for the development and maintenance of healthy bones.” She also notes that it plays a crucial role in supporting immune health and ensuring proper function of muscles and brain cells.
Let’s explore what vitamin D3 is, why it is vital for your health, and the recommended dosage for supplementation when necessary.
What is vitamin D3?
Vitamin D3, scientifically known as cholecalciferol, is one of the two primary forms of vitamin D. The other form, vitamin D2 (ergocalciferol), is derived from plant sources and fortified foods. Susie states that vitamin D3 is naturally synthesized in the skin upon exposure to sunlight.
Classified as a fat-soluble vitamin, vitamin D3 can dissolve in fat and is stored in the body’s fatty tissues and liver. This means that it does not get quickly eliminated through urine, as water-soluble vitamins like vitamin C do. While this storage capability allows the body to maintain vitamin D levels over time, it also indicates that excessive intake can lead to accumulation in the body.
Although D2 and D3 share similar chemical structures and functions, Jill Weisenberger, a registered dietitian and author of “Prediabetes: A Complete Guide,” notes that research indicates vitamin D3 is more effective at raising and sustaining blood concentrations of vitamin D “and keeping levels elevated longer.”
According to Susie, sunlight exposure remains the most efficient way to boost vitamin D3 levels. However, various factors such as limited sunlight, regular use of sunscreen, age, darker skin pigmentation, and geographic location can hinder some individuals from generating enough vitamin D naturally. Furthermore, “Individuals with absorption issues such as Crohn’s disease, celiac disease, and cystic fibrosis may also face deficiencies,” states Weisenberger. Susie adds that a body mass index over 30 can be linked to lower vitamin D levels since fat cells can trap vitamin D.
For individuals in these situations, supplementation could be beneficial. Additionally, increasing dietary sources can aid in meeting vitamin D needs. “Prime natural sources include fatty fish like trout, salmon, tuna, mackerel, and fish liver oils,” says Susie. Other sources include eggs, beef liver, and fortified foods such as milk and cereals. Weisenberger also points out that UV-exposed mushrooms provide vitamin D.
What does vitamin D3 do for the body?
Regardless of its source, vitamin D3 is crucial for the absorption of calcium and phosphorus—minerals essential for developing and sustaining strong bones and teeth. As Weisenberger explains, without adequate vitamin D, bones may become brittle or misshapen, resulting in conditions such as rickets in children and osteomalacia or osteoporosis in adults.
Moreover, vitamin D3 bolsters the immune system. Weisenberger notes that it helps modulate the inflammatory response in the body and enhances immune cells’ efficiency in combating pathogens.
Research also indicates additional benefits on muscle strength, mood stabilization, and possible protection against infections, including COVID-19, along with major illnesses such as cancer, cardiovascular and respiratory diseases, diabetes, and dementia, according to Susie.
How much vitamin D3 should I take daily?
While vitamin D deficiency is significantly more common than excessive intake, maintaining an appropriate balance is crucial, as “excess vitamin D can result in elevated calcium levels in the blood, kidney disease, deposits of calcium in soft tissues, heart disease, and even death,” warns Weisenberger.
For this reason, the National Institutes of Health Office of Dietary Supplements recommends that most individuals aged 1 to 70 consume about 15 micrograms (600 international units or IU) of vitamin D daily, while those over 70 generally need approximately 800 IU.
The NIH also states that the upper limit should not exceed 4,000 IU per day from all sources—food, beverages, and supplements—unless under medical supervision. “Always disclose any vitamin D supplementation to healthcare providers,” Susie advises, “particularly if you are taking multiple supplements or medications.”
