Nutrition and Hair Loss: What the Evidence Actually Supports
The supplement section of any health store has more hair-related products than almost any other category — and a lower average evidence quality. Here's the honest breakdown of what nutritional interventions actually support hair health, and the distinction between supplementing deficiencies versus supplementing in the absence of them.
01The deficiency principle
Most nutritional supplements for hair only matter when there's an actual deficiency. This distinction is critical: correcting a vitamin D deficiency can meaningfully improve hair shedding; supplementing vitamin D in someone with normal levels does essentially nothing. Same for iron, zinc, and B12.
02The nutrients worth testing
| Nutrient | Hair relevance | Who should supplement |
|---|---|---|
| Ferritin (iron storage) | Low ferritin is directly associated with diffuse shedding | Women especially; anyone with heavy shedding; vegetarians |
| Vitamin D | Receptors in follicles; deficiency linked to hair cycle disruption | Most people in northern latitudes, especially in winter |
| Zinc | Supports follicle cell proliferation | Those on restrictive diets or with confirmed deficiency |
| B12 | Cell division in active follicles | Vegans, vegetarians, older adults |
| Biotin | Only relevant if genuinely deficient | Very few adults with normal diets — deficiency is rare |
Get tested before you supplement. A basic panel (ferritin, 25-OH vitamin D, zinc, B12, TSH) tells you what's actually low. Supplementing blind costs money and in some cases (iron, zinc) carries risk of excess. The $70 lab panel is a better investment than $70/month of untargeted supplements.
03Protein: the one non-deficiency factor that matters
Hair is made of keratin, a protein. Inadequate total protein intake — common during caloric restriction, crash diets, or GLP-1 medication use — triggers telogen effluvium: the body deprioritizes hair growth resources. Adequate protein (1–1.2g per pound of goal body weight, for most adults) is the one nutritional factor that matters even without a diagnosed deficiency.
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