Vitamin D is involved in more than 100 biochemical reactions and plays a crucial role in bone metabolism, immune regulation, muscle function, and inflammation control. Low vitamin D levels have been linked to anxiety, depression, insomnia, joint pain, autoimmune conditions, thyroid dysfunction, and increased cancer risk.
Sunlight is the primary source of vitamin D. Ultraviolet B rays stimulate the skin to produce vitamin D3, which is later activated by the liver and kidneys. This process becomes less efficient with age, putting older adults at higher risk for deficiency. Skin color also affects vitamin D production; people with darker skin require longer sun exposure than those with lighter skin to produce the same amount.
Season and clothing significantly affect vitamin D synthesis. During summer, when more skin is exposed, only a few minutes of midday sun may be sufficient. In winter, most of the body is covered, leaving 5–10 percent of skin exposed, which may require 1–2 hours of midday sun to generate adequate vitamin D.
Vitamin D is a fat-soluble vitamin absorbed in the small intestine. Adequate absorption depends on bile secretion and pancreatic enzyme activity. People with pancreatic insufficiency, chronic pancreatitis, reduced bile flow, gallbladder removal, or other fat-malabsorption conditions may struggle to maintain sufficient vitamin D levels. Certain cholesterol-lowering medications, especially bile acid sequestrants, can further reduce vitamin D absorption.
Low vitamin D is not solely a sun-exposure issue. Age, season, skin color, digestive health, and medication use all play important roles.
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