Vitamin D Deficiency: Signs, Risks, and How to Fix It
Vitamin D deficiency is the most common nutritional deficiency in the US, affecting an estimated 40% of adults. Most people have no idea. Here's what you need to know.
Why Vitamin D Matters
Vitamin D is actually a hormone, not just a vitamin. It regulates calcium absorption, immune function, mood, muscle strength, and hundreds of gene expressions.
Signs You May Be Deficient
- Fatigue that doesn't improve with sleep
- Frequent illness (colds, infections)
- Bone or muscle pain
- Low mood, especially in winter
- Hair thinning
Who's Most at Risk
- People who work indoors all day
- Anyone living above 37° latitude (most of the US north of San Jose)
- People with darker skin tones (melanin reduces UV absorption)
- Overweight individuals (Vitamin D is fat-soluble and gets sequestered)
How to Check
A simple blood test: 25-hydroxyvitamin D. Optimal is 40-60 ng/mL. Below 20 is deficient.
What to Do
- Sunlight: 15-30 minutes midday on arms and legs (without sunscreen) 3-4x weekly
- Supplement: 2,000-4,000 IU daily for most deficient adults (get tested first)
- Food sources are minimal: fatty fish, egg yolks, fortified milk
Always test before supplementing high doses. Consult your doctor.
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