Vitamin A improves thyroid function in premenopausal women
Subclinical hypothyroidism is characterized by moderately elevated TSH, thyroid-stimulating hormone, and normal T4. It may progress to hypothyroidism, which can cause high blood pressure, high cholesterol and other cardiovascular problems [1].
Although prescription levothyroxine has shown clinical benefits [1], it may also have substantial adverse effects [2]. Natural ways to support thyroid health would therefore be useful. A 2014 study [3] suggests vitamin A supplementation may help regulate thyroid function.
Eighty-four healthy premenopausal women aged 17–50 received vitamin A, one capsule containing 25,000 IU as retinyl palmitate daily, or placebo for four months. Blood tests before and after measured thyroid function. Women of reproductive age were studied because they are vulnerable to low vitamin A and thyroid dysfunction [4].
Of the 84 women, 56 had obesity, BMI 30–35, and 28 did not, BMI 18.5–24.9. Those with obesity received vitamin A or placebo; all 28 without obesity received vitamin A, without a corresponding placebo group.
After four months, researchers noted the following changes across the three groups:
| Measure | With obesity, vitamin A | With obesity, placebo | Without obesity, vitamin A | p value |
| TSH (milli-international units) |
Decrease of 29.9% (3.08 to 2.16) |
Decrease of 11.6% (3.71 to 3.28) |
Decrease of 33.3% (3 to 2) |
0.004 |
| T3 (nmol/L) |
Increase of 38.2% (2.04 to 2.82) |
Increase of 17.3% (2.31 to 2.71) |
Increase of 61.1% (1.88 to 3.03) |
0.001> |
| T4 (nmol/L) |
Decrease of 16.5% (124.37 to 103.88) |
Decrease of 23.5% (118.86 to 90.95) |
Decrease of 22.6% (123.40 to 95.63) |
0.001> |
The most important finding was normalization of TSH in the vitamin A groups to 0.3–3.0 milli-international units, the range recommended by the American Association of Clinical Endocrinologists [4]. The placebo group did not achieve normal TSH.
The stated reference range for T3 is 1.1–3.0 nmol/L and for T4, 64–155 nmol/L [5].
The article suggests that 25,000 IU vitamin A as retinyl palmitate may be effective for mild thyroid imbalance and reduce subclinical hypothyroidism risk before menopause. However, further research is needed to assess iodine levels and clarify possible differences in vitamin A’s thyroid effects between men and women.
[1] Papi G, Uberti ED, Betterle C, Carani C, Pearced EN, Bravermand LE, Roti E: Subclinical hypothyroidism. Curr Opin Endocrinol Diabetes Obes 14:197–208, 2007
[2] Biondi B, Fazio S, Carella C, Amato G, Cittadini A, Lupoli G, Sacca L, Bellastella A, Lombardi G: Cardiac effects of long term thyrotropin-suppressive therapy with levothyroxine. J Clin Endocrinol Metab 77:334–338, 1993
[3] Farhangi MA. The effect of vitamin A supplementation on thyroid function in premenopausal women. J Am Coll Nutr 2012 Aug;31(4):268-74
[4] Baskin HJ, Cobin RH, Duick DS, Gharib H, Guttier RB, Kaplan MM, Segal RL: American Association of Clinical Endocrinologists. American Association of Clinical Endocrinologists medical guidelines for clinical practice for the evaluation and treatment of hyperthyroidism and hypothyroidism. Endocr Pract 8:457–469, 2002.
[5] American College of physicians, Normal Lab Values Reference Table. Accessed April 16, 2015