It was a beautiful day today in Brussels! So I was stubbornly sitting on my sunlit balcony (despite the not-all-that-comfortable 6°C) hoping to get those sun rays to do its magic and for the VitaminD to start flowing in my veins and it got me wondering… How fast does VitD synthesize in our skin, and we really capable of making it ourselves, or is it just another hoax to make us crave that sunny days even more? As it often turns out, making sure your body has enough VitD is a matter of lifestyle rather than location.
So I got into reading about it and… Phew – turns out that we humans are indeed able to synthesize it in our own skin upon exposure to UV B sunlight. Those are the sun rays with wavelength between 280–315nm or in other words – the ones that do not burn your skin, as compared to UV A which make us tan instead of burn, if you are lucky, but also wrinkle and age.
But the VitD synthesized in our skin, or the one we intake with foods and supplements is not biologically active, so roasting would not do the trick on its own. The more important work is being done by our liver and kidneys where the preVitD produced in our skin, is converted gradually into a biologically active molecule – calcitriol. Many cells have receptors for calcitriol on the membranes of their nuclei. Once this receptor binds the active form of VitD, it becomes an activated transcription factor – a protein which is able to alter the expression of specific genes. In most cases, the genes activated are the ones involved in the regulation of calcium uptake in the intestines, making sure that bones are properly maintained by the cells in charge of this, which are in their turn dependent and use calcium for their proper functioning. Depending on the cell type which absorbs the VitD, it can activate other genes too – one of the most often influenced family of genes are related to the immunity – in the production and specialization of white blood cells.
Still, how long of an exposure is enough to get our dose of VitD? According to the NIH – between 5 and 30 minutes twice per week is enough to acquire a moderate but sufficient amount of VitD precursor in the skin, which can be stored in the liver for up to 15days after its synthesis. This is less than a quarter of the time required for a very mild sunburn, so don’t go roasting in the sun thinking it’s good for you! Also because the UV A which penetrates along can damage your skin much more for the same amount of time, and if you rely on sunscreen creams, most of them block the UV B rays either way. So basically if you have a morning walk to work, or sip your coffee on the terrace, or grab your lunch on that green spot close to work, you’d be more than fine with your VitD production, without risking damage to your skin and you will probably feel much more relaxed simply from enjoying those few minutes a day of sunshine. It has also been shown that VitD plays a key role in the prevention of depression.
But what if you live somewhere where there’s not enough sun shining? I feel for you – proper sunny days can be scarce here in Belgium too. But you can always get your required VitD doses from foods which contain it naturally or (as a last resort) as a food supplement. Keep in mind tho, that most of the multivitamin pills contain less than optimal VitD concentrations! Mushrooms for example are able to synthesize VitD themselves too, which makes them the perfect source for it. Many fish (especially the more fatty ones) are a great source of VitD precursors, such as salmon, tuna, and sardines. Also rich in it are egg yolks and beef livers.
And as a bottom line, it turns out you don’t need to despair if you don’t have too much sunlight in your region (at least when it comes to your VitD production), because according to some latest studies, geographical longitude does not correlate as straightforwardly as scientists thought with the ability to produce own VitD. VitD-deficiencies have been recorder in plenty in sunny countries as well, so a little bit of care for your own personal health and food regime in this case can make wonders too! For my part, I’m sure I got just about enough sun to boost my VitD production today and knowing it already makes me feel better! 🙂