It all starts in the brain, not in bones: The first and foremost sign of vitamin D deficiency

Contrary to popular belief, the earliest signs of vitamin D deficiency often manifest in the brain, not the bones. Mood swings, anxiety, and irritability can signal slipping vitamin D levels, as the nutrient is crucial for serotonin production. These mental and emotional symptoms appear before physical discomfort due to the brain's rapid response to nutrient deficiencies.