Vitamin D is essential for your body!.........  And sunlight seems to be in short supply.

Vitamin D is required for strong bones. Calcium and phosphorus are essential for developing the structure and strength of your bones, and you need vitamin D to absorb these minerals. Even if you eat foods that contain a lot of calcium and phosphorus, without enough vitamin D, you can't absorb them into your body.

It helps prevent high levels of the parathyroid hormone. This hormone reabsorbs bone tissue, which makes bones thin and brittle.

It is  also thought to help strengthen your immune system and may prevent depression.

Good sources of Vitamin D are:

Sunlight! Yes, UV rays are also damaging so try to get them before the sun is at it’s strongest in the summer months. Supplements may be a useful addition during winter months when we are wrapped up.

Eggs

Oily fish such as salmon, sardines

Dairy products

Tuna

Beef, liver

Cod liver oil

http://www.elephantjournal.com/2016/01/10-reasons-to-take-vitamin-d-during-the-winter/