Vitamin D’s importance extends far beyond calcium absorption and bone density. Emerging evidence reveals that vitamin D deficiency selectively weakens type II fast-twitch muscle fibers—the very fibers responsible for explosive movements and rapid postural corrections that prevent falls. When vitamin D binds to receptors in muscle cells, it activates pathways for muscle protein synthesis and regulates the calcium machinery essential for contraction. Without adequate vitamin D, these critical fast-twitch fibers atrophy while slow-twitch fibers remain largely unaffected, explaining why deficiency correlates with increased fall risk in older adults. However, while animal mechanistic studies provide robust evidence, human reversal trials have yielded mixed results, partly because researchers have failed to stratify participants by baseline deficiency status. Read the full article on GMJ Newsroom.
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