Sunlight is necessary to make Vit D3, which is produced under the skin. Small amounts of Vit D are found in oily fish, eggs, sweet potato, vegetable oils, milk, beef and liver and Swiss cheese. Herbs that contain Vit D are nettles, alfalfa and parsley.
We need sufficient sunlight to synthesise Vit D and it is a common deficiency particularly as we lose more daylight hours as we move into winter. In kinesiology we can test to see if you need Vit D.
Why do we need enough VIT D? It maintains strong bones and teeth, helps support the immune system (therefore prevents many diseases), maintains normal muscle function and is needed for healthy thyroid function.