Vitamin A Intake Impacts Thyroid Function
Vitamin A supplementation may reduce the risk of subclinical hypothyroidism in pre-menopausal women, according to a new randomized double-blind controlled trial. Approximately 4.6 percent of the U.S. population has hypothyroidism and the incidence increases with age. Previous research shows that vitamin A regulates thyroid hormone metabolism and inhibits thyroid-stimulating hormone (TSH) secretion. Obese individuals have an increased risk of developing subclinical hypothyroidism.
The subjects included 84 healthy women between 17 and 50 years of age, including 56 obese women with a body mass index (BMI) 30-35 kg/m2, and 28 non-obese women with a BMI of 18.5-24.9 kg/m2. The researchers assigned the obese women to receive 25,000 IU vitamin A as retinyl palmitate daily or placebo for four months. The non-obese women received vitamin A daily. The researchers measured serum concentrations of thyroid TSH, total thyroxine (T4), total triiodothyronine (T3), retinol-binding protein and transthyretin (transports thyroxine and retinol) at the beginning of the study and again after the four-month intervention period.
The investigators determined that vitamin A supplementation significantly reduced serum TSH and increased T3 (active thyroid hormone) levels in both obese and non-obese subjects. In the obese subjects that received vitamin A, the researchers found a significant decrease in serum retinol-binding protein, but no significant change was seen in serum transthyretin. Serum T4 decreased in all three groups after the intervention period.
The investigators concluded, “Serum TSH concentrations in vitamin A-treated subjects were significantly reduced; therefore, vitamin A supplementation might reduce the risk of subclinical hypothyroidism in premenopausal women.”
Farhangi MA, et al. J Am Coll Nutr. 2012;4:268-74.
More Articles at www.DrMeletis.com
