What nutrient deficiencies are linked to hair loss in hypothyroidism?

Nutrient Deficiencies Linked to Hair Loss in Hypothyroidism

The primary nutrient deficiencies associated with hair loss in hypothyroidism are iodine, iron, selenium, zinc, and vitamin D, with iodine and iron being the most directly implicated in thyroid dysfunction itself. 1

Iodine Deficiency

• Iodine deficiency is the most fundamental nutrient deficiency causing hypothyroidism worldwide, and hypothyroidism itself is a well-recognized cause of hair loss 1
• Worldwide, iodine deficiency remains the most common cause of hypothyroidism, though in industrialized nations Hashimoto's disease predominates 1
• Maternal hypothyroidism from iodine deficiency specifically increases risk of congenital cretinism with associated growth failure 1
• The recommended iodine intake is 150 μg per day, with sources including iodized salt, seafood, and dairy products 2

Iron Deficiency

• Iron deficiency directly impairs thyroid metabolism and hormone synthesis, making it a critical deficiency to address in hypothyroid patients with hair loss 1
• Iron is essential for thyroid peroxidase activity and thyroid hormone synthesis 1
• The guideline evidence specifically states that "healthy thyroid function depends on an adequate provision of selenium and iron at any age" and that "iron deficiency impairs thyroid metabolism" 1
• Checking for iron deficiency is recommended as an aggravating factor in patients with hair loss 1

Selenium Deficiency

• Selenium is required for conversion of T4 to the active T3 hormone through Type 1 5'-deiodinase, a selenoenzyme 1
• Adequate selenium provision is necessary for healthy thyroid function at any age 1
• Selenium-rich foods include Brazil nuts, fish, eggs, and whole grains, with supplementation of 50-70 μg/day potentially beneficial for some patients with autoimmune thyroiditis 2

Zinc Deficiency

• Zinc deficiency can both result from and contribute to hypothyroidism, creating a bidirectional relationship 3
• Zinc and other trace elements are required for synthesis of thyroid hormones, and deficiency can result in hypothyroidism 3
• Conversely, thyroid hormones are essential for zinc absorption, so hypothyroidism can cause acquired zinc deficiency 3
• Hair loss attributed to hypothyroidism may not improve with thyroxine alone unless zinc supplements are added 3
• Consider zinc supplementation at 15 mg/day if deficient 2

Vitamin D Deficiency

• Vitamin D deficiency is common in hypothyroidism and may contribute to hair loss 2
• While vitamin D's role is more established in alopecia areata (an autoimmune condition), vitamin D supplementation should be considered if levels are low in hypothyroid patients 1
• Vitamin D has established roles in normal hair follicle function, with the vitamin D receptor being critical for hair cycling 1

Clinical Approach

When evaluating hair loss in a hypothyroid patient, screen for:

• Thyroid function status (TSH, free T4) to ensure adequate thyroid hormone replacement 1
• Iodine status through 24-hour urinary iodine excretion (normal: 100-300 μg/24hr) 1
• Iron studies including serum ferritin, as iron deficiency directly impairs thyroid metabolism 1
• Selenium levels if available, given its role in T4 to T3 conversion 1
• Zinc levels, particularly if hair loss persists despite adequate thyroid hormone replacement 3
• Vitamin D levels (25-OH vitamin D), targeting at least 30 ng/mL 2

Important Caveats

• The hair loss may not resolve with levothyroxine alone if concurrent nutrient deficiencies exist, particularly zinc deficiency 3
• Multiple deficiencies often coexist in hypothyroid patients, requiring comprehensive nutritional assessment 1, 2
• Ensure thyroid medication is taken on an empty stomach, 30-60 minutes before eating, to optimize absorption 2
• Avoid excessive iodine intake (>300 μg daily) as it can paradoxically worsen thyroid function in some individuals 2