Although we can get vitamin D from certain food sources (fatty fish like salmon, sardines, and mackerel) as well as fortified foods, most of the vitamin D in our bodies comes from the sun, something many northerners in the US don't see for a good four to six months in the winter. Vitamin D is actually made by our bodies. Once it gets absorbed into our skin, it is processed into a hormone that can then be used for all the important functions it plays in our bodies. We need vitamin D because it has a symbiotic relationship with calcium. Without adequate levels, we cannot absorb calcium and this is bad for bone growth and health. I really like the graph below that explains what happens when we don't have enough vitamin D and some of the causes of a deficiency (yes, wearing too much sunscreen can be bad!).
Before I jump to the supplements I love, the optimal way to raise vitamin D is with the sun! Most of us don't live in sunny places year-round, but when there is sun get out and absorb it! If you are fair-skinned, try to get 15-30 minutes a day of sun unexposed before you apply sunscreen.
In the winter it is crucial to supplement no matter how much sun you get in the summer because it will not last for 6 months. I love Thorne Research supplements. They are a company devoted to keeping strict standards on the quality of their supplements and this shows in the minimal additives in their pills. Another option that I am currently using is Nordic Naturals. I take the omega-3 pill with vitamin D in it that way I am getting a healthy dose of my fats too! I like the pill form because it is easy to remember. Slurping cod liver oil is another great way to get vitamin d and omega 3's as well though and it really doesn't taste bad at all, especially if you get lemon flavor. I recommend the brand Carlson's.
The reason I am very stringent about the brands is because most other companies give us forms of medicine we cannot utilize (example: getting vitamin D2 instead of the correct form d3). Or, they will barrage the medicine with so many additives we are barely getting any of the vitamin! Thorne and Nordic Naturals doesn't do this, though. SO for Vitamin D or any kind of supplements you need, I highly recommend their products.
Last winter I was very deficient in vitamin D and it definitely affected my mood and energy levels. So I took 5,000 IU with dinner (usually with an avocado since it is fatty and vitamin D is fat soluble) and also supplemented with cod liver oil once a day. Between those two things, I was able to raise my vitamin D levels from the mid-20s which is deficient to 53 and cure the mild depression. 53 is right in the middle range and a good level for someone living so far north. Now when I am on vacation I try to get as much exposure as possible especially since I am so dark complected and do not burn easily. Also, it is harder for darker people like myself to get vitamin D because it takes the sun's rays longer to penetrate into our skin (see chart above-- darker= more melanin). So for once fair-skinned people should be happy!
Since my vitamin d level is still in the normal range this winter, I just supplement with the omega-3d pill by Nordic Naturals that I stated above. Although supplementing is optimal in the north, getting sun is the best way to raise levels. This is because vitamin D is not actually a vitamin, but a hormone our bodies make when we get sun. When our bodies feel the rays it turns on the process to secrete vitamin D. We can also get some from foods like salmon and egg yolks, but the sun is the most natural and original way.
I hope this article was informative and if you are feeling down, this will encourage you to start supplementing. A blood test is also a great place to start to see where your level lies, but I guarantee if you live in the north, you are most likely deficient. Also, it is very very hard to have too much vitamin d so if you don't feel like getting a blood test, supplement with a smaller dose like I currently am doing. Hurray for good moods even without the sun!