Vitamin D: From Skin to Bone | The Most Misunderstood Vitamin❤️❤️

The video covers the following key aspects of Vitamin D:
Definition and Misconception: Initially named "Vitamine" due to its essential role in life and assumption of containing nitrogen (1:09), the 'e' was dropped when later discoveries showed other vitamins lacked nitrogen (2:48). Vitamin D is unique because the body can synthesize it, unlike other vitamins, making it more akin to a hormone (3:38-3:43, 30:40).
Synthesis in Skin: Vitamin D is synthesized in the skin when exposed to specific ultraviolet B (UVB) rays from sunlight (8:40).
The process starts with 7-dehydrocholesterol in the epidermis (4:50), which has a double bond on its seventh carbon in the B-ring (6:52).
UVB light, specifically with a wavelength between 320-280 nanometers, provides the necessary energy to break this double bond (11:47-12:03, 14:01).
This action opens the B-ring of the cholesterol structure, converting it into cholecalciferol, also known as Vitamin D3 (13:30-13:55, 15:56).
The video clarifies the common misconception that early morning sunlight is effective; only midday sun (10 AM to 1 PM) contains sufficient UVB for synthesis (12:06-13:11).
Activation in Liver and Kidney:
Liver: Cholecalciferol (inactive Vitamin D) travels to the liver, where the enzyme 25-hydroxylase adds a hydroxyl group (-OH) to the 25th carbon, forming 25-hydroxycholecalciferol, also known as calcidiol (17:08-18:48). This form is used for storage and transport (29:09-29:14).
Kidney: Calcidiol then moves to the kidneys. The enzyme 1-alpha-hydroxylase, activated when blood calcium levels are low and parathyroid hormone (PTH) levels are high, adds another hydroxyl group to the first carbon (20:18-22:58). This final step produces 1,25-dihydroxycholecalciferol, or calcitriol, which is the active form of Vitamin D (23:06-25:22).
Function: Active Vitamin D (calcitriol) primarily works in two places (29:17-29:34):
Intestines: It promotes the synthesis of proteins in the intestinal walls that are essential for absorbing calcium and phosphorus from digested food into the bloodstream (31:19-34:50).
Bones: It helps maintain blood calcium levels by facilitating the deposition of calcium onto bones, thereby increasing bone density and strength (35:56-36:14). If blood calcium is low, it can also stimulate the release of calcium from bones to maintain balance (36:38-37:00).
Deficiency: A deficiency in Vitamin D leads to insufficient calcium absorption and bone mineralization, resulting in:
Rickets in children, characterized by soft and weakened bones during the growing stage (37:02-37:07, 37:42-38:03).
Osteomalacia in adults, where existing bone density decreases due to calcium withdrawal, making bones weak and prone to fractures (37:07-37:16, 38:05-38:15).
Why Vitamin D behaves like a true hormone
Regulation of calcium & phosphate metabolism
Rickets vs Osteomalacia (conceptual + clinical clarity)
Why Vitamin D deficiency is so common in India
Effect of melanin / skin color on Vitamin D synthesis
Sunlight vs supplements — what science really says
NEET-oriented concepts & PYQ-linked explanations
Common myths and mistakes about Vitamin D
🎯 Who is this video for?
NEET / medical / nursing / pharmacy students
Class 9–12 biology learners
Competitive exam aspirants
Anyone interested in true health science & awareness
This video is not about memorizing facts —
it’s about understanding Vitamin D deeply, logically, and scientifically.
👉 If you want clarity instead of confusion, watch till the end.
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Because real science should be understood, not feared.