The same protein, keratin, makes up both your hair and nails, which means the nutrients that strengthen one tend to strengthen the other. A combination of adequate protein, specific vitamins and minerals, and healthy fats gives your body the raw materials it needs to produce strong, resilient keratin. Getting these nutrients from food is the most reliable approach, though certain supplements have clinical evidence behind them for people with specific deficiencies or brittle nails.
Protein and Amino Acids Come First
Keratin is a protein, and your body can’t build it without a steady supply of amino acids. The amino acid cysteine is especially important: it makes up 7% to 20% of keratin’s total amino acid content and forms the sulfur bonds that give hair its elasticity and nails their hardness. If your diet is low in protein, your body prioritizes vital organs over hair and nails, which is why severe calorie restriction or very low-protein diets often lead to thinning hair and peeling nails.
Good sources of cysteine and other keratin-building amino acids include eggs, poultry, fish, legumes, and dairy. Garlic and onions also contribute: garlic provides a compound that converts into cysteine during digestion, while onions supply it alongside vitamin C and zinc, both of which support keratin formation.
Collagen Peptides for Brittle Nails
Collagen supplements have some of the more concrete clinical evidence for nail health specifically. In a trial where participants took 2.5 grams of collagen peptides daily for 24 weeks, nail growth rate increased by 12% and the frequency of broken nails dropped by 42%. After the treatment period ended, 88% of participants still saw improvement four weeks later, suggesting the benefits aren’t purely temporary. Sixty-four percent achieved a noticeable clinical improvement in brittle nails overall.
Collagen peptides provide the amino acids glycine, proline, and hydroxyproline, which your body uses as building blocks for connective tissue. If brittle, peeling nails are your main concern, collagen has stronger evidence than most other supplements.
Biotin: Useful for Deficiency, Not a Cure-All
Biotin is the most heavily marketed supplement for hair and nails, but the reality is more nuanced. It plays a genuine role in keratin production by acting as a helper molecule for enzymes involved in fatty acid synthesis and amino acid processing. The daily adequate intake for adults is 30 micrograms, and most people get enough from a balanced diet that includes eggs, nuts, seeds, and whole grains.
Supplemental biotin, typically sold in doses of 500 to 1,000 micrograms, shows the clearest benefit in people who are actually deficient or who have diagnosed conditions like brittle nail syndrome, where doses of 300 to 3,000 micrograms daily are used. For people without a deficiency, lab studies on normal hair follicle cells show that extra biotin doesn’t stimulate additional growth or thickening. In other words, more isn’t better if you’re already getting enough.
One important caution: high-dose biotin supplements can interfere with lab tests. The FDA has issued warnings that biotin can cause falsely low troponin results (the test used to detect heart attacks) and can skew thyroid panels. If you take biotin and need blood work, let your doctor know or stop the supplement a few days beforehand.
Iron and Zinc Deficiencies Cause Real Damage
Iron deficiency is one of the most common nutritional causes of hair shedding worldwide. When iron stores drop too low, your body shifts resources away from hair follicles, triggering a type of diffuse hair loss where strands fall out evenly across the scalp. This is particularly common in women with heavy periods, vegetarians, and frequent blood donors. Red meat, lentils, spinach, and fortified cereals are reliable food sources, and pairing plant-based iron with vitamin C (like lemon juice on lentils) significantly improves absorption.
Zinc supports the cell division that drives both hair and nail growth. Low zinc levels are linked to hair shedding, slow nail growth, and white spots on the nails. Oysters are the single richest food source, but beef, pumpkin seeds, chickpeas, and cashews all contribute meaningful amounts.
Healthy Fats Lock In Moisture
Dry, brittle hair and nails that crack easily can signal a lack of essential fatty acids. Omega-3 fats help maintain the lipid barrier that keeps your hair cuticle smooth and your nail plate flexible. Without enough dietary fat, nails become rigid and prone to splitting, while hair loses its natural shine and feels straw-like.
Fatty fish like salmon, mackerel, and sardines are the most efficient sources. Walnuts, flaxseeds, chia seeds, and avocados provide plant-based omega-3s and other healthy fats. Even just a tablespoon of olive oil in your daily cooking contributes to the fat intake your body needs to keep hair and nails hydrated from the inside out.
Vitamins A, D, and E Play Supporting Roles
Vitamin A supports the production of sebum, the natural oil that coats your scalp and keeps hair from drying out. Sweet potatoes, carrots, and leafy greens are excellent sources. However, vitamin A is one of the few nutrients where excess intake actively causes hair loss. Staying within the recommended daily amount (700 to 900 micrograms for adults) is important, and people taking supplements should check whether multiple products overlap.
Vitamin D receptors are present in hair follicles, and low vitamin D levels are associated with hair shedding. Since many people are deficient, especially those living in northern latitudes or spending most of their time indoors, this is worth checking with a simple blood test. Vitamin E acts as an antioxidant that protects the fats in your hair and nail structures from oxidative damage. Sunflower seeds, almonds, and hazelnuts are concentrated sources.
Selenium: A Little Goes a Long Way
Selenium is a trace mineral that supports antioxidant defenses in hair follicles, but it has one of the narrowest safety windows of any nutrient. Daily intake above 400 micrograms can cause selenosis, which ironically triggers significant hair shedding along with fatigue, nausea, and joint pain. Animal studies confirm this pattern: mice given excessive selenium developed intense hair loss, while those with moderate intake did not. A single Brazil nut contains roughly 70 to 90 micrograms of selenium, so eating just one or two a day is plenty. Stacking selenium from multiple supplement sources is the most common way people accidentally overdo it.
Rosemary Oil for Scalp Health
For a topical approach, rosemary oil has clinical backing. A six-month trial comparing rosemary oil applied to the scalp against a standard 2% hair-growth treatment found no significant difference between the two groups in hair count at the end of the study. Both groups saw meaningful increases in hair count by month six, though neither showed results at three months. This suggests rosemary oil works, but requires patience. Mixing a few drops into a carrier oil like coconut or jojoba and massaging it into the scalp a few times per week is the typical approach.
Set Realistic Timelines
Scalp hair grows about 1 centimeter per month on average, and fingernails grow just over 3 millimeters per month. This means any nutritional change you make today won’t show visible results in your hair for two to three months, and nail improvements take a similar timeline since the new, stronger nail has to physically grow out from the base. The collagen trial mentioned earlier ran for 24 weeks before measuring final results, which gives you a realistic sense of the commitment involved.
If you’re experiencing sudden or patchy hair loss, nails that are separating from the nail bed, or changes that came on without an obvious cause like a crash diet or major stress, those patterns point toward something beyond nutrition, such as thyroid dysfunction, autoimmune conditions, or hormonal shifts, and are worth investigating with bloodwork rather than supplements alone.