Primary source of vitamin D for human beings is

The primary source of vitamin D for human beings is the sun. Vitamin D3 (cholecalciferol) is synthesized in the skin when it is exposed to ultraviolet-B (UVB) radiation from sunlight. Specifically, 7-dehydrocholesterol in the epidermis absorbs UVB rays and is converted into previtamin D3, which then isomerizes into vitamin D3 [2]. This process is so efficient that vitamin D is often referred to as the 'sunshine vitamin'. While dietary sources exist, few foods naturally contain significant amounts of vitamin D. Citrus fruits are primarily sources of vitamin C, and green vegetables do not provide substantial vitamin D. Yeast can produce vitamin D2 (ergocalciferol) when irradiated, but sunlight remains the most significant natural source for human synthesis. Factors like skin pigmentation and geographic latitude can influence the efficiency of this production.

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1. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC8418216/