Hair Loss: Possible Medical Causes

Hair loss is a common concern that affects people of all ages and genders, and for many individuals, losing hair causes significant psychological distress and diminished quality of life. While genetics and aging are widely recognized contributors, a range of medical conditions and nutritional deficiencies can also disrupt normal hair growth. Hair follicles are among the most rapidly dividing structures in the body and depend on robust blood supply and nutrient availability, which is why researchers have studied the relationship between micronutrient status and hair loss since the 1960s.

From thyroid dysfunction to iron deficiency, various medical factors can interrupt the hair growth cycle, leading to increased shedding, diffuse thinning, or distinct bald patches. Identifying whether a treatable underlying condition is contributing to hair loss is an important first step, because addressing the root cause often leads to meaningful improvement.

Thyroid hormones have a well-established connection to hair health, and both overactive and underactive thyroid conditions can trigger hair thinning. Hypothyroidism, in particular, may cause hair loss along with prolonged shedding (telogen effluvium) and hair that becomes dry, brittle, and dull. Iron deficiency is another significant contributor: when iron stores are depleted, hemoglobin production falls, reducing oxygen delivery to cells throughout the body, including those responsible for hair growth and repair.

Hormonal imbalances, especially involving testosterone and its derivative dihydrotestosterone (DHT), contribute to pattern hair loss in both men and women. Research has also identified an inverse relationship between vitamin D levels and several forms of non-scarring hair loss, including telogen effluvium, androgenetic alopecia, and alopecia areata. Zinc deficiency is another recognized factor, as zinc is essential for cell reproduction and protein synthesis, both of which are critical for healthy hair follicle function.

Laboratory testing is worth considering when hair loss goes beyond the normal daily shedding of 50 to 100 hairs, particularly if the onset is sudden or the pattern differs from typical hereditary thinning. Testing is especially valuable when hair loss is accompanied by other symptoms such as fatigue, unexplained weight changes, cold sensitivity, or shifts in energy levels. Screening for iron deficiency in individuals presenting with hair loss is a well-supported clinical practice, as treatment for iron deficiency, whether or not anemia is present, often enhances hair loss treatment outcomes.

Women experiencing hair loss during periods of hormonal transition, such as menopause or the postpartum period, may benefit from comprehensive hormone and nutrient testing. Testing is also recommended when hair loss has a rapid onset, as this pattern more often suggests an underlying medical condition rather than genetic predisposition.

Lab results can identify treatable underlying causes that, once addressed, may lead to meaningful hair regrowth. Abnormal TSH levels may indicate hypothyroidism or hyperthyroidism, both of which can cause thinning; hair loss associated with thyroid dysfunction typically reverses after hormone levels are normalized, though regrowth may take time. Iron studies showing low ferritin or depleted iron stores point to a potentially reversible cause, as most iron-related hair loss is not permanent.

Testosterone levels, when elevated alongside genetic sensitivity, may contribute to pattern hair loss through conversion to DHT. Interestingly, individuals with androgenetic alopecia may not have higher circulating testosterone but may have elevated levels of the enzyme that converts testosterone to DHT, or hair follicles that are inherently more sensitive to these hormones. Low vitamin D levels may represent a contributing factor, particularly in diffuse thinning. Normal test results do not exclude hair loss from other causes, including genetic predisposition, stress-related shedding, or medical conditions not covered by the tests ordered.

Optimal nutrition supports healthy hair growth and can help prevent deficiency-related shedding. A balanced diet that includes iron-rich foods (spinach, lentils, lean meats, dried fruit) and vitamin C-rich foods (which enhance iron absorption) provides the nutritional foundation for healthy follicles. Stress management is important because chronic stress can disrupt hormonal balance and trigger telogen effluvium, a condition in which hair follicles prematurely enter the resting phase and shed.

Gentle hair care practices can protect follicles that may already be under stress. Avoiding tight hairstyles, excessive heat styling, and harsh chemical treatments reduces mechanical and chemical damage to fragile hair. Adequate sun exposure or vitamin D supplementation can help maintain optimal vitamin D levels, which research links to healthier hair growth cycles. When nutrient deficiencies or hormonal imbalances are identified through testing, targeted treatment often produces the best results when combined with these supportive lifestyle measures.