Vitamins types and their sources functions and deficiency
Vitamins are organic micronutrients the body needs in small amounts to function properly, but since the body can’t synthesize most of them on its own, they have to come from diet (or, for vitamin D, sunlight). There are 13 recognized vitamins, split into two categories based on how the body absorbs and stores them: water-soluble and fat-soluble.
Water-soluble vs. fat-soluble: the key difference
Water-soluble vitamins (vitamin C and the eight B vitamins) dissolve in water and aren’t stored long-term in the body — excess amounts are excreted in urine. That means regular intake matters more, since reserves don’t build up.
Fat-soluble vitamins (A, D, E, and K) are absorbed with dietary fat and stored in the liver and fatty tissue. Deficiency tends to develop more slowly, but high-dose supplementation carries more risk of buildup to harmful levels than with water-soluble vitamins.
The 13 vitamins at a glance
| Vitamin | Key role | Main food sources |
|---|---|---|
| Vitamin A | Vision, immune function, cell growth | Liver, dairy, carrots, sweet potatoes |
| Vitamin C | Antioxidant, collagen synthesis, immunity | Citrus fruits, peppers, broccoli |
| Vitamin D | Calcium absorption, bone health | Fatty fish, fortified dairy, sunlight |
| Vitamin E | Antioxidant, cell membrane protection | Nuts, seeds, vegetable oils |
| Vitamin K | Blood clotting, bone metabolism | Leafy greens, broccoli, eggs |
| B1 (Thiamine) | Carbohydrate metabolism, nerve function | Whole grains, legumes, pork |
| B2 (Riboflavin) | Energy production, organ health | Eggs, dairy, spinach |
| B3 (Niacin) | Energy metabolism, cholesterol balance | Poultry, fish, nuts |
| B5 (Pantothenic acid) | Energy metabolism, hormone production | Broccoli, mushrooms, eggs |
| B6 (Pyridoxine) | Red blood cells, nerve signaling | Poultry, fish, whole grains |
| B7 (Biotin) | Hair, skin, and nail health | Eggs, salmon, nuts |
| B9 (Folate) | DNA synthesis, red blood cells | Leafy greens, beans, fortified grains |
| B12 (Cobalamin) | Red blood cells, nervous system | Meat, fish, eggs, dairy |
For the full breakdown of each vitamin’s forms, functions, food sources, and deficiency signs, see our dedicated guides on water-soluble vitamins and fat-soluble vitamins.
Why vitamins matter for hair and scalp health
A handful of vitamins have a particularly direct connection to hair: biotin (B7) and vitamin B12 support the metabolic processes hair follicles rely on, vitamin C is required to synthesize the collagen that supports hair structure, and vitamin D deficiency has been linked to certain types of hair shedding. That said, supplementing a vitamin you’re not actually deficient in generally won’t accelerate hair growth — the benefit shows up when correcting a real deficiency, not from taking more than the body needs.
Recognizing a possible deficiency
Common general signs across multiple vitamin deficiencies include fatigue, hair thinning or shedding, brittle nails, skin changes, and slow wound healing — though the specific pattern varies by vitamin. If you suspect a deficiency, a blood test is the reliable way to confirm it rather than guessing from symptoms and self-prescribing supplements, since some vitamins (particularly the fat-soluble ones) can cause harm at excessive doses.