Science for All | What is UV-B light and what is its role in vitamin D synthesis?

Light that we can see is a type of electromagnetic radiation. The entire electromagnetic spectrum consists of waves of different wavelengths, ranging from very long wavelength radio waves to short wavelength gamma rays. In descending order of wavelength, these are radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. In this, what we call light includes the triad of infrared, visible and ultraviolet radiation. Ultraviolet light, or UV light, sorts light of wavelengths beyond what we humans can see (10 nanometers to 400 nanometers). UV light is further subdivided based on its properties as we humans experience it into different types. These include UV-A light with a wavelength of 315-400 nanometers; UV-B light, spanning 280-315 nanometers; and UV-C, with a range of 100-280 nanometers. Under this UV-B light is interesting because it is in the range that our bodies are sensitive to. As light from the sun passes through the atmosphere, the mixture of ozone, water vapor, oxygen and carbon dioxide in the atmosphere absorbs all UV-C and most UV-B light. UV-A filters through.

Fortunately, or perhaps because of the way we’ve evolved, UV-A is the least harmful of this type of radiation. UV-C is quite harmful but is completely filtered out by the ozone layer. UV-B penetrates the skin briefly, causing delayed sunburn, and also aids in the synthesis of vitamin D. When exposed to sunlight, a compound called 7-dehydroxycholesterol (7-DHC), also known as provitamin D ₃is converted into previtamin D ₃† This in turn isomerizes into vitamin D ₃† The previtamin D ₃ and vitamin D ₃ absorb UVB light and produce substances that are beneficial to the body. For this reason, vitamin D is also referred to as the sunshine vitamin.

Vitamin D is known to help regulate calcium and phosphate metabolism. For example, a deficiency of vitamin D can lead to diseases such as soft bones in children and osteoporosis in adults. Vitamin D supplements and sensible exposure to sunlight can help prevent these conditions.

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