Thyroid Dysfunction Links To Age-Related Macular Degeneration

Thyroid Dysfunction Links To Age-Related Macular Degeneration

The thyroid gland is like a pilot that controls your metabolism. Metabolism is the process in which your body transforms food into energy. Your thyroid gland is in charge of releasing specific hormones to keep your metabolism working optimally. When this gland is compromised, there can be a variety of systemic complications which may include the development of macular degeneration

Recent research shows decades of evidence that supports how thyroid dysfunction may link to AMD (age-related macular degeneration). AMD afflicts approximately 11 million Americans and is the number one disorder that causes blindness to date. Unless there are discovered ways to stop this disease, it is expected to escalate to 22 million by 2050. 

As researchers continue to study AMD, clues such as the thyroid connection that may help treat and possibly cure macular degeneration in the near future.

Understanding the Thyroid

Before exploring the connection between AMD and thyroid dysfunction, it is important to understand the thyroid a little more. This way you can look for signs that may indicate a thyroid compromise and then be able to take action if needed. 

The thyroid is responsible for messengering hormone response which affect every cell and every organ in the body. According to Michigan Medicine, reported by the University of Michigan, these hormones: 

  • Regulate the rate at which calories are burned, affecting weight loss or weight gain.
  • Can slow down or speed up the heartbeat.
  • Can raise or lower body temperature.
  • Influence the rate at which food moves through the digestive tract.
  • Control the way muscles contract.
  • Control the rate at which dying cells are replaced.

It is easy to see how important this small gland is to overall systemic health and why an imbalance may contribute to age-related macular degeneration.  

Thyroid Imbalance Signs that May Lead to AMD

Some people can go through years of struggling with various health symptoms that are never linked to a thyroid dysfunction. There are two types of dysfunction categories: hyperthyroidism (overactive) and hypothyroidism (under-active). The Cleveland Clinic lists some possible indications of thyroid dysfunction:

Symptoms of an overactive thyroid (hyperthyroidism) can include:

  • Experiencing anxiety, irritability and nervousness
  • Having trouble sleeping
  • Losing weight
  • Having an enlarged thyroid gland or a goiter
  • Having muscle weakness and tremors
  • Experiencing irregular menstrual periods or having your menstrual cycle stop
  • Feeling sensitive to heat
  • Having vision problems or eye irritation

Symptoms of an under-active thyroid (hypothyroidism) can include:

  • Feeling tired (fatigue)
  • Gaining weight
  • Experiencing forgetfulness
  • Having frequent and heavy menstrual periods
  • Having dry and coarse hair
  • Having a hoarse voice
  • Experiencing an intolerance to cold temperatures

These symptoms would need to be chronic or persistent to warrant a thyroid dysfunction consideration. If you feel you are presenting any of these as a constant struggle do let your doctor  know and request your thyroid be tested. In the meantime, recent research compilation shows how thyroid dysfunction may link to AMD.

The Thyroid Connection

As the thyroid gland holds great status regarding overall systemic function, researchers began to look at how a compromise of this gland might affect vision. The retina is one of the most oxygen required tissues in the body, any form of oxidative stress could negatively affect its activity. 

Mitochondrial production of ATP (adenosine triphosphate which forms adenosine diphosphate, energy for physiological processes such as muscular contraction) via oxidative metabolism is essential for retinal functioning and the thyroid plays an important role in this process. When the thyroid is compromised, ATP functioning can affected. Thyroid dysfunction can be caused by a variety of things including:

  • Virus
  • Bacteria 
  • Genetic Disorder
  • Iodine Deficiency
  • Medical Treatments

Once the thyroid is compromised, medical intervention can help regulate hormone production. However, these medicines which are synthetic versions of thyroid hormone thyroxine (T4), may do more than that.

The thyroid connection to macular degeneration was found to be associated with increased hormone levels. Although hyperthyroidism (overactive) has shown to be the most corresponding to AMD development, hypothyroidism (under-active) can also be a risk factor. Overall, researchers found that when either one of these dysfunctions were treated with anti-thyroid drugs, a significant protection factor was discovered.

According to results of a recent study (June 2020) by researchers at The Department of Cell Biology, University of Oklahoma which was published in Investigative Ophthalmology & Visual Science (IOVS), 

“Treatment with antithyroid drug protected photoreceptors from oxidative damage and cell death induced by NaIO3, and preserved retinal function. The outer nuclear layer thickness and cone photoreceptor density were significantly increased in mice treated with antithyroid drug. [] The number of TUNEL-positive cells, the number of the DNA damage marker p-γH2AX-positive cells and 8-OHdG-positive cells, and Müller glia activation were significantly reduced in mice treated with antithyroid drug.”

The study concluded:

“Suppression of TH signaling protects photoreceptors from oxidative damage and cell death induced by NaIO3 and may represent a strategy for photoreceptor protection in AMD.”

This study shows a direct correlation in rodent models, however another study from 2016 reported the results of ten years of human research (2334 participants). The study was titled ‘Thyroid Dysfunction and Ten-Year Incidence of Age-Related Macular Degeneration’ and published in Clinical and Epidemiologic Research which concluded that, 

“Overt hyperthyroidism was independently associated with an increased risk of incident AMD. Thyroxine [main hormone produced by the thyroid] usage in older adults was also positively associated with incidence of AMD.”

Thyroxine was also found to be a factor in a 2015 study of 5,573 participants by researchers at Erasmus University Medical Center, Rotterdam, The Netherlands published in BMC Medicine (BioMed Central) which concluded,

“We find an increased risk of incident AMD in subjects with higher FT4 levels, even in those with a normal thyroid function and when excluding thyroid medication users. This implies an intrinsic (that is, not exogenous [external cause]) deleterious [harmful] effect of thyroid hormone on AMD. We also find an association between higher FT4 [free thyroxine thyroid-stimulating hormone] levels and retinal pigment alterations, suggesting that thyroid hormone could even play a role in the early stage of development of AMD.” 

If you are experiencing thyroid dysfunction talk to your ophthalmologist about being checked for macular degeneration. It is important to not lose sight of other risks while dealing with an acute situation at the same time.