What Causes an Increase in Vitamin D Levels?

December 14, 2025 •

3 min read

According to the National Institutes of Health, the most effective natural way to increase vitamin D levels is through sun exposure, as the skin produces vitamin D3 in response to ultraviolet B (UVB) radiation. However, this is not the only factor, as diet and supplementation also play significant roles in maintaining healthy vitamin D levels.

Quick Summary

The main factors for increasing vitamin D are sunlight exposure, which triggers skin synthesis, and dietary intake from specific foods and fortified products. Supplements are also a powerful and reliable method to boost levels, especially for those with limited sun exposure or dietary restrictions.

Key Points

Sunlight is Key: Your body produces vitamin D when your skin is exposed to UVB radiation, but production is affected by latitude, season, time of day, and skin tone.
Boost with Diet: Few foods are naturally high in vitamin D, but options like fatty fish, egg yolks, and some mushrooms can contribute. Many dairy products and cereals are also fortified.
Supplements for Consistency: Vitamin D supplements, particularly D3, are a reliable and effective way to ensure consistent intake, especially for those with limited sun exposure.
Balancing Sun Exposure: Moderating sun exposure is crucial to balance vitamin D synthesis with skin cancer risk, making other sources important.
Darker Skin Requires More Sun: People with darker skin have more melanin, which reduces the skin's ability to synthesize vitamin D from sunlight, requiring more exposure to achieve the same level.
Supplementation vs. Diet: While diet can contribute to vitamin D levels, supplements offer a much more reliable and measurable dose, which is particularly beneficial for those with confirmed deficiencies.

Sunlight Exposure: The Primary Driver of Vitamin D Production

For most people, the most significant source of vitamin D is exposure to sunlight, earning it the nickname the "sunshine vitamin". When UVB rays from the sun strike the skin, they convert a cholesterol compound into vitamin D3. The amount of vitamin D produced depends on several factors:

Time of day: The sun's rays are most direct, and therefore most effective for vitamin D production, between 10 a.m. and 3 p.m..
Geographical location: The closer you are to the equator, the more vitamin D your body can produce year-round due to the higher intensity of UVB radiation. Conversely, people in northern latitudes may produce very little vitamin D from sunlight during winter.
Skin tone: Melanin, the pigment that determines skin color, competes with the compound that produces vitamin D for absorbing UVB radiation. As a result, individuals with darker skin require significantly more sun exposure to produce the same amount of vitamin D as those with lighter skin.
Clothing and sunscreen: While crucial for preventing skin cancer, covering up or applying sunscreen with an SPF of 8 or higher can significantly reduce or block vitamin D synthesis. A few minutes of unprotected exposure may be enough to start production, but moderation is key to balancing risks.

Dietary Sources of Vitamin D

While few foods naturally contain significant amounts of vitamin D, certain items can help increase your levels. Consuming dietary fat alongside vitamin D can also enhance its absorption in the gut.

Naturally Rich Foods

Fatty fish and seafood: Salmon, tuna, mackerel, and sardines are among the best natural food sources.
Egg yolks: The yolks contain a small amount of vitamin D.
Beef liver: A modest source of vitamin D.
Mushrooms: Some mushrooms, particularly those treated with UV light, contain vitamin D2.

Fortified Foods

Because natural sources are limited, many common food products are fortified with vitamin D. Always check the nutrition label for confirmation.

Milk (cow's milk and plant-based alternatives): Most cow's milk in the U.S. is fortified, as are many non-dairy milks like soy and almond milk.
Cereals and orange juice: Many brands offer fortified breakfast cereals and orange juice.
Yogurt and cheese: Some dairy products are enriched with vitamin D.

Supplementation: A Reliable Method

For those with limited sun exposure or dietary options, or who have specific medical conditions, supplements are a consistent and effective way to increase vitamin D. Vitamin D supplements come in two main forms:

D2 (ergocalciferol): Derived from plants.
D3 (cholecalciferol): Derived from animal sources, typically more effective at raising blood vitamin D levels.

Supplements are especially important during winter months in northern climates when sun exposure is insufficient. Consulting a healthcare professional can help determine the correct dosage for your individual needs. For quality and purity, look for supplements that have been independently tested and certified.

Comparison of Vitamin D Sources


Source	Pros	Cons	Reliability	Considerations
Sunlight	Free, most effective natural method	Dependent on season, latitude, time of day; skin cancer risk with overexposure; affected by sunscreen	Variable	Requires balanced approach to avoid skin damage. Not viable for all populations or locations year-round.
Dietary Sources	Part of a balanced diet, provides other nutrients	Few natural sources are rich in vitamin D; content can be variable; not all foods are fortified	Moderate	Must consistently choose specific fortified or naturally rich foods. Absorption is fat-dependent.
Supplements	Consistent and measured dosage; reliable source	Requires consistent adherence; risk of toxicity with excessive intake	High	Best method for specific deficiencies, limited sun exposure, or during winter. D3 is often more effective than D2.

Conclusion

Several factors contribute to an increase in vitamin D levels, with sunlight exposure, diet, and supplements being the most prominent. While sun exposure is the primary natural source, factors like geography, season, and skin tone significantly influence its effectiveness. Dietary intake from fortified foods and fatty fish provides a complementary source. However, for consistent and reliable results, particularly for individuals at risk of deficiency, supplementation is often the most effective method. A multi-faceted approach combining safe sun exposure, a vitamin-D-rich diet, and targeted supplementation can help ensure adequate levels for optimal health, bone mineralization, and immune function. Consult a healthcare provider to determine the best strategy for your specific health needs.

Authoritative Link

For more detailed information on vitamin D's role in health and disease, consult the National Institutes of Health's fact sheet: Vitamin D - Health Professional Fact Sheet.

Frequently Asked Questions

Experts suggest that 5 to 30 minutes of sun exposure, especially between 10 a.m. and 3 p.m., at least twice a week to the face, arms, legs, or back can be sufficient for many people. However, this varies based on skin tone, location, and season.

For most people, it is challenging to obtain sufficient vitamin D from diet alone, as very few foods naturally contain significant amounts. A combination of fortified foods, natural sources like fatty fish, and often supplementation is necessary.

Supplements are often necessary, especially for people with limited sun exposure, darker skin tones, or those living in northern latitudes during winter. They provide a reliable way to maintain adequate levels when diet and sun are insufficient.

Vitamin D2 (ergocalciferol) is plant-derived, while vitamin D3 (cholecalciferol) is typically animal-derived and synthesized in the skin from sunlight. Research suggests that vitamin D3 is more effective at raising and maintaining overall vitamin D levels in the body.

Yes, sunscreen with an SPF of 8 or higher can block the UVB rays that trigger vitamin D synthesis. However, since most people don't apply it perfectly or consistently, some vitamin D production still occurs.

It is not possible to develop vitamin D toxicity from sun exposure alone. The body has a built-in mechanism that limits the amount of vitamin D it produces, and excessive sun exposure degrades vitamin D into inactive forms.

As people age, their skin becomes less efficient at synthesizing vitamin D from sunlight. This, along with potentially reduced sun exposure, can increase the risk of deficiency in older adults, making supplementation more important.