What frequency produces vitamin D?

December 22, 2025 •

4 min read

Vitamin D, often called the “sunshine vitamin,” is essential for human health, with research showing that cutaneous synthesis provides the majority of the body's needs for most people. This vital process is triggered by a very specific and narrow frequency of light: ultraviolet B (UVB) radiation.

Quick Summary

Vitamin D production in the skin is triggered by ultraviolet B (UVB) radiation within the 290 to 320 nanometer wavelength range, peaking in efficiency around 297-300 nm. The amount produced depends on factors like time of day, season, latitude, skin color, and exposed skin area.

Key Points

UVB is the Key: Vitamin D synthesis is specifically activated by ultraviolet B (UVB) radiation, not other parts of the light spectrum.
Optimal Wavelength: The most effective wavelength for vitamin D production is in the narrow band of 290-320 nanometers, with peak efficiency near 297-300 nm.
Midday Sun is Potent: The midday hours (roughly 10 a.m. to 3 p.m.) are the most efficient time for vitamin D synthesis due to higher UVB intensity.
Factors Affect Production: Latitude, season, skin pigmentation, age, cloud cover, and sunscreen all significantly influence how much vitamin D you produce from sun exposure.
Sunlight is Self-Regulating: The body has a natural mechanism to prevent vitamin D toxicity from too much sun exposure, converting excess previtamin D3 into inactive compounds.
Supplements for Reliability: For those with limited sun access or high-risk factors, dietary intake or supplements are a reliable way to ensure adequate vitamin D levels.

Understanding the Ultraviolet Spectrum

To understand what frequency produces vitamin D, one must first grasp the basics of the ultraviolet (UV) light spectrum. UV light is an electromagnetic wave with a shorter wavelength than visible light. It is divided into three main categories based on wavelength: UVA, UVB, and UVC.

UVA (320–400 nm): Has the longest wavelength and can penetrate deep into the skin's dermis. It plays a primary role in skin aging and wrinkles but does not effectively stimulate vitamin D production.
UVB (290–320 nm): Has a shorter wavelength than UVA and is mostly absorbed by the epidermis, the skin's outer layer. It is this specific band that is responsible for sunburns but also triggers vitamin D synthesis.
UVC (100–290 nm): The shortest and most harmful UV wavelength, but it is completely absorbed by the Earth's ozone layer and does not reach the surface.

The Critical Wavelength Range for Vitamin D

For vitamin D production to occur, the skin needs exposure to the UVB portion of the spectrum. Specifically, research shows that UVB radiation in the 290 to 320 nanometer (nm) range is the active frequency band. Within this range, the peak efficiency for converting 7-dehydrocholesterol in the skin to previtamin D3 occurs between 297 nm and 300 nm. This process is highly dependent on the intensity of UVB reaching the Earth's surface, which is influenced by numerous factors, including the sun's angle and atmospheric conditions.

Factors Influencing Vitamin D Synthesis from Sunlight

Several variables determine how much vitamin D your body can produce from sun exposure:

Time of day: Midday hours (roughly 10 a.m. to 3 p.m.) offer the most potent UVB radiation, as the sun is at its highest point. Morning and late afternoon sunlight contains a lower proportion of UVB due to the angle of the sun's rays filtering through the atmosphere.
Season: Synthesis is highly seasonal. During winter in latitudes above approximately 35 degrees, the sun's angle is too low for enough UVB to penetrate the atmosphere, effectively creating a “vitamin D winter”.
Latitude: Locations closer to the equator receive more intense, year-round UVB exposure, allowing for consistent vitamin D production. Those living in higher latitudes face a greater risk of deficiency in colder months.
Skin pigmentation: Melanin, the pigment in darker skin tones, acts as a natural sunscreen and reduces the efficiency of vitamin D production. As a result, individuals with darker skin require significantly more sun exposure to produce the same amount of vitamin D as lighter-skinned individuals.
Cloud cover and pollution: Both clouds and air pollution can significantly reduce the amount of UVB radiation reaching the ground, impacting synthesis.
Age: The skin's ability to produce vitamin D decreases with age, making older adults more susceptible to deficiency.
Sunscreen and clothing: Sunscreen and clothing that covers the skin effectively block UVB rays, inhibiting vitamin D production.

Natural vs. Supplemental Vitamin D Production

While sun exposure is the body's primary natural source of vitamin D, it's not always a viable option for everyone. Supplements offer a controlled, reliable alternative, especially for those in high-risk groups. Here is a comparison of vitamin D production methods:


Feature	Vitamin D from Sunlight (UVB)	Vitamin D from Supplements
Source	Natural skin synthesis triggered by UVB radiation.	Oral intake of cholecalciferol (D3) or ergocalciferol (D2).
Safety	Requires cautious, timed exposure to avoid skin damage like sunburn and increased skin cancer risk. The body self-regulates against producing toxic amounts.	Safe and effective when taken as directed. High doses can lead to toxicity (hypercalcemia).
Efficiency	Highly variable based on season, latitude, skin tone, and time of day.	Consistent and reliable dosage regardless of external factors.
Accessibility	Limited by geography, weather, clothing, and lifestyle. Not always available year-round.	Easily accessible and available globally. Independent of sun exposure.
Duration in Blood	The vitamin D3 produced in the skin may last longer in the bloodstream compared to ingested vitamin D.	Clears from the blood faster than vitamin D synthesized in the skin.

The Importance of a Balanced Approach

Due to the risks of excessive sun exposure and the unreliability of solar synthesis for many populations, a combination of safe sun exposure and dietary or supplemental intake is often recommended. For those in high-risk groups, including the elderly, those with darker skin, and individuals living in northern latitudes, supplements are often necessary to maintain optimal vitamin D levels. The Skin Cancer Foundation offers further information on balancing sun protection and vitamin D needs.

Conclusion

The frequency that produces vitamin D is the specific range of ultraviolet B (UVB) radiation between 290 and 320 nanometers. This photochemical reaction is highly efficient and is the body's primary natural source of vitamin D. However, the process is impacted by a multitude of factors, including the sun's position, location, skin type, and lifestyle choices. While sun exposure is a powerful trigger for vitamin D synthesis, it must be balanced with sun-safety practices to mitigate the risks of skin damage. For many, supplements provide a reliable and consistent way to ensure adequate levels, complementing, and sometimes replacing, sun-derived production.

Frequently Asked Questions

The specific wavelength range that produces vitamin D in the skin is ultraviolet B (UVB) radiation, spanning approximately 290 to 320 nanometers (nm). The optimal peak for this synthesis occurs around 297-300 nm.

For people living at latitudes above approximately 35 degrees, it is generally not possible to get sufficient vitamin D from the sun during winter months. The sun's angle is too low, and the atmosphere filters out most of the necessary UVB radiation.

Individuals with darker skin have more melanin, which acts as a natural sunscreen and absorbs UVB radiation. This reduces the skin's ability to produce vitamin D, meaning darker-skinned individuals need more sun exposure time to synthesize the same amount as those with lighter skin.

No, you cannot get toxic levels of vitamin D from sun exposure alone. The body has a built-in regulatory system that converts excess previtamin D3 into inactive photoproducts, preventing overproduction.

The best time for vitamin D synthesis is typically midday, between 10 a.m. and 3 p.m., when the sun's UVB rays are most intense. Outside of these hours, the sun's rays are less effective for this purpose.

Even with significant sun exposure, factors like age, skin tone, and geographical location can impact your ability to produce enough vitamin D. It is best to have your blood levels checked by a doctor to determine if you need supplements, which provide a reliable source.

The time needed varies greatly depending on skin tone, location, and time of year. As a general guide, 5 to 30 minutes of midday sun exposure to your face and arms a few times a week can be enough for some, but listen to your body and avoid sunburn.