Hypothyroidism may contribute to color blindness
A study conducted in Frankfurt and Main, Germany, and published in the Journal of Neuroscience found that laboratory mice with thyroid hormone deficiencies tended to produce less pigment in their retinas, even as adults.
Researchers said that this association between adult-onset hypothyroidism and a decreased ability to see certain colors likely extends to humans.
An estimated 5 percent of the U.S. population suffers from hypothyroidism, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Women are more likely than men to have the condition.
In the new study, neuroscientists and endocrinologists analyzed the amounts of two pigments, called opsins, found in the retinal cone cells of rodents' eyes. It had been previously established that during physical maturation, thyroid hormone deficiency can lead to an imbalance of UV/blue opsin and green opsin, which are sensitive to short- and long-wave light, respectively.
To delineate the pigments in color-detecting cone cells, the team used antibodies that only bind to one opsin or the other. Using fluorescence microscopy, researchers could see that lab rodents with hypothyroidism had far more UV/blue opsin in their retinas, compared to green opsin.
The study's authors concluded that thyroid hormone appears to control the balance of opsins in the eyes, even into adulthood. They noted that when the lab animals' hormone levels returned to normal, the levels of opsins tended to equalize.
In humans, a number of conditions and treatments can cause hypothyroidism. These include inflammation of the thyroid gland, Hashimoto's thyroiditis, certain medications, radiation therapy and partial or complete thyroidectomy, according to the NIDDK.
Symptoms of the condition include weight gain, fatigue, sensitivity to cold, joint aches, brittle hair and a decreased ability to sweat, the health resource adds.