I worked at a clinic that had a staff psychiatrist. He was great and let me ask him all kinds of fun questions*. I was working on some patient data sets and asked him why he wanted to add a Vitamin D test to all the blood workups. I assumed maybe it was a side effect of the medication that most of our patients were taking. However, he said most people in our geographic region are chronically low on Vitamin D.
How weird! We have sunlight every day! We're famous for our fog, but we're not fighting Seattle for any titles. Or Chicago for that matter. (33 min of sunlight in December, that is CRAZY).
Fun fact - vitamin D isn’t actually a vitamin. A vitamin is any organic compound required for nutrition that can’t be made by our bodies. We can make a lot of things but some stuff we have to eat in order to run our systems. Vitamin D is a component of calcium metabolism. Calcium is, of course, used for bones but it’s also a messenger molecule and used for communication of muscular and neurological activity. There are several versions of Vitamin D, but lets talk about D3.
What do we need it for?
Vitamin D3 is the kind we need for stable bones and muscles. We can take in calcium by eating it (dairy and dark green veggies, 'sup kale) but we need some D3 to help absorb it and make it ready to use. D3 also regulates the amount of calcium in our blood stream. If there isn't enough calcium cruising around, your body will start taking it from its main stash, your bones.
Where do we get it?
We can actually make D3, or at least its starting material. The kickoff to D3 is 7-dehydrocholesterol and our skin makes a lot of it. However, it has to be photochemically (fancy word for sun activated!) stimulated in order to turn into D3. This is where the 20 minutes in the sun per day recommendation comes from. We need to our skin to be exposed to the sun so we can kick off D3 generation in our skin cells. We're kind of like plants in that we need the sun to make important stuff! So cool!
Unfortunately, we need direct exposure to stimulate it. We can’t get that when sitting in front of a window (or TV or computer monitor) but we can get it from a tanning bed (though, not a good idea). Sun exposure also has pleasant effects and we may have evolved serotonin production to go along with D3 generation to ensure it happens. (Fun fact: people who die in summer have more serotonin in their brains than those who die in winter.)
How much sun do we need?
A quick google search seems to show that the recommendation is for 20 minutes of unprotected sun exposure per day. Another article suggests 30 minutes. D3 is broken down almost as soon as its made so it makes sense to me that getting some sun multiple times throughout the day is good idea. I’m not sure why we’d make it and then dump it quickly, more research required! Perhaps we make a lot because we were once covered in hair and generating it took more sun exposure (even though we were outside WAY more than now). Having D3 ready to go makes sense since we likely were eating outdoors and consuming calcium which our body would want to absorb and put to work. Dumping quickly might make sense too as we were outside all day and if you aren't using it, you can't let it hang out and affect your blood pressure especially as we don't have a storage method.
What about sunscreen?
OK, so this is kind of wild! I was super surprised to read that sunscreen, with as low as factor/SPF 8, can block vitamin D production up to 50% or more, higher SPFs up to 97%. That seems like a huge amount! So yay that sunscreen is working? But boo that it isn’t helping. If you wear a moisturizer with SPF 15 then you might be blocking your D3 production for the day. Skin cancer is clearly a concern, however, we have cleverly evolved a way to prevent skin cancer during these necessary and "sensible" sun exposure times.
So SPF is one reason some of us might be low on our Vitamin D and lots of us stay inside and don't get enough "sensible exposure" but I wonder if there's more going on? More research required! And in the mean time, go outside and play!
Carlsson, A., L. Svennerholm, and B. Winblad. "Seasonal and circadian monoamine variations in human brains examined post mortem." Acta psychiatrica Scandinavica. Supplementum 280 (1979): 75-85.
Lambert, G. W., et al. "Effect of sunlight and season on serotonin turnover in the brain." The Lancet 360.9348 (2002): 1840-1842.
Crissey, Susan D., et al. "Serum concentrations of lipids, vitamin D metabolites, retinol, retinyl esters, tocopherols and selected carotenoids in twelve captive wild felid species at four zoos." The Journal of nutrition 133.1 (2003): 160-166.
Matsuoka, Lois Y., et al. "Chronic sunscreen use decreases circulating concentrations of 25-hydroxyvitamin D: a preliminary study." Archives of Dermatology 124.12 (1988): 1802-1804
Lips, Paul, Natasja M. Schoor, and Renate T. Jongh. "Diet, sun, and lifestyle as determinants of vitamin D status." Annals of the New York Academy of Sciences 1317.1 (2014): 92-98.
* Q: Why are schizophrenic visions so terrifying? Why aren't there unicorns and joy? A: There are! They often manifest as God speaking and no one seeks help for happy visions.