Because vitamin D is an important nutrient for the proper function of the immune system, it should be monitored and optimized on a regular basis, especially for people with any kind of autoimmune issue. Vitamin D is also one of the nutrients to heal leaky gut.[reference]
The best way to get vitamin D is direct mid-day sunlight on bare skin — such as at times when your shadow is shorter than you are. But make sure you don’t get burned, because that can cause skin cancer. In order for skin to generate vitamin B, the UVB rays of the sun needs to hit the skin. It can also go through light clothing. But it can not go through glass.
You don’t want to get sun through glass, because you don’t have any benefits from the UVB rays generating vitamin D. But you do get UVA rays being able to penetrate glass and even giving you a tan. However, UVA rays are not beneficial in generating vitamin D, and may even be detrimental by destroying vitamin D. That is why Dr. Mercola says to avoid getting tan through the window. [reference]
Certainly it would be fine to sit by the window and may in fact be beneficial in that light from sun can strengthen the circadian rhythm and fight seasonal affected depression. But you shouldn’t be in a position for such a long duration where you are feeling heat from the sun through the window to the point where you are starting to get a tan.
When you are outside in nature without the separation of glass (as nature intends for our body to be), the UVA and UVB rays are in balanced and you get the optimal vitamin D you need without overdosing. The UVB generates the vitamin D. While the UVA destroys it and tans your skin if you get too much. Tanning darkens your skin naturally so that a natural feedback to slow down the vitamin D production when it doesn’t need it. People with dark skins will need to be out in the sun longer to generate the same amount of vitamin D.
Depending on where you live, there are certain months of the year where you get no vitamin D from the sun at all. The UVB rays can only generate vitamin D when the sun is greater than 50 degrees above the horizon. Otherwise, the UVB will bounce off the atmosphere.
To determine when the sun is above this angle, look at the “altitude” column on this site.
Cod Liver Oil
So in winter, many people may need to supplement with vitamin D. While cod liver oil had been recommended by many as a source of vitamin D, new update from Dr. Mercola suggests that cod liver oil may cause an unfavorable vitamin D to vitamin A ratio because it contains too little D and too much A. Depending on the particular cod liver oil, it may have excessive vitamin A and not enough vitamin D.
In terms of vitamin A, it is better to take beta-carotene and let you own body make the amount of vitamin A it needs from that, rather than taking vitamin A — which can become toxic in excess.
However, WestonAPrice.org “have pointed out that concerns about vitamin A toxicity are exaggerated” and suggests using Fermented Cod Liver Oil and list Green Pastures Cod Liver Oil as a possible brand to look at. However, Chris Kresser found some update on that, and recommends Extra Virgin Cod Liver Oil from Rosita Real instead.
Sally Fallon writes defending cod liver oil.
If you are going to take cod liver oil, get one with as low vitamin A and as high vitamin D as possible. Dr. Mercola says Carlson has the best ratio.
Do not confuse cod liver oil or Omega 3 fish oil. The latter being mainly for omega-3 DHA/EPA supplementation and does not contain vitamin A or D.
Or you can get some vitamin D from salmon. But it is difficult to eat enough salmon to get the amount of vitamin D one needs. Plus there is the danger of mercury in salmon when over-consumed.
Personally, I do feel that cod liver oil and salmon alone is not a sufficient source of vitamin D, so now I take vitamin D tablets during those winter months. It is also preferred to take vitamin K2 when taking vitamin D.
Whenever supplementing with vitamin D, you should retest your levels. Because if blood levels get up to greater than 100 ng/ml, it is getting to toxic levels. Optimal levels of vitamin D is 50-70 ng/ml of 25 Hydroxy D test (according to Dr. Mercola)
To learn more about Vitamin D watch this webinar by Dr. David Anderson who says that people need not be afraid of the sun …
https://youtu.be/GhuAwyJcpWM