If you Google “vitamins for hair growth,” you’ll get a million results pushing the same three names: biotin, vitamin D, and iron. The marketing makes them sound like magic. The reality is more nuanced — and knowing which one (if any) you actually need can save you money and frustration.
Biotin: the most overhyped
Biotin is in every hair supplement, every hair gummy, every “grow your hair faster” product on the market. It’s become synonymous with hair growth. And for most people, it does absolutely nothing.
Here’s why: biotin deficiency is extremely rare in people eating a normal diet. Your gut bacteria produce it. It’s in eggs, nuts, salmon, sweet potatoes, and dozens of other common foods. Unless you have a rare genetic condition, are on certain medications, or have severe gut issues, you’re almost certainly getting enough from food.
Supplementing biotin when you’re not deficient is like pouring water into a full glass. It just overflows. Your body excretes what it doesn’t need.
Worse: high-dose biotin interferes with lab tests. It can give false readings on thyroid panels, cardiac tests, and other important bloodwork. If you’re taking biotin, stop for at least 48 hours before any blood draw.
Vitamin D: genuinely important
This one matters. Vitamin D receptors exist on hair follicles, and research shows low levels are associated with hair loss. Deficiency is extremely common — especially if you live in a northern city like Chicago where winter sunlight is insufficient for skin synthesis.
Get tested. If you’re below 40 ng/mL, supplement with vitamin D3 (1,000–5,000 IU daily depending on your levels). Take it with a fatty meal for better absorption. Most people in Chicago need to supplement at least from October through April.
Results take time. Expect 3–6 months of consistent supplementation before seeing hair improvement.
Iron: the one most women are missing
Iron deficiency is the most common nutritional deficiency worldwide and one of the top correctable causes of hair thinning in women. Heavy periods, vegetarian diets, intense exercise, and recent pregnancy are all risk factors.
The key number is ferritin — your stored iron. Many doctors consider anything above 12 ng/mL “normal,” but dermatologists want to see 40+ for healthy hair growth. If your ferritin is in the 12–40 range, you might not be anemic, but your hair might be starving.
Test specifically for ferritin, not just hemoglobin. Supplement with iron bisglycinate if you’re low (it’s gentler on the stomach). Take with vitamin C, away from coffee and dairy.
The bottom line
Don’t guess. Don’t just buy whatever supplement has the prettiest packaging. Get bloodwork done: ferritin, vitamin D, and a complete thyroid panel. Fix what’s actually low. Ignore what’s not.
For the topical side of hair health — products, treatments, and professional care — book at Reverie. We’ll handle what goes on your hair while your doctor handles what goes in your body.
