Can we get Vitamin D all year long by sun exposure?

25 April 2021

This is a misunderstood topic, but an important one. First, Vitamin D does not come from the sunlight itself, but it is the product of a chemical reaction between specific molecules (7-dehydrocholesterol) located under your skin and UVB radiation. UVB radiation is a special type of high energy light which has a wavelength in the range 280–315 nm. This is at the far end of the visible spectrum towards the blue light, but UVB is invisible to the human eye.

In order for your skin to produce Vitamin D there must be UVB light, however one problem is that UVB is not always present in the sunlight that reaches us (depending mainly on the season, the time of day, and where you live). Moreover, the amount of UVB available during each specific day of the year varies all year long!

So how can we know when to expose our skin to the sun in order to produce Vitamin D? A good rule of thumb is to look at the location of the sun in the sky: the highest it is in the sky, the more likely there will be UVB. For example, around noon is usually a good time to get UVB.

But this is only true for certain times of the year, and it is highly dependent of your exact location. For example, if you live in New York, you cannot produce any Vitamin D from sunlight during several months each year, even if it is very sunny outside. Why? This will be the topic of the future post. Stay tuned for more!

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