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Did you know that the season in which you were born could actually impact your health? Recent research has suggested that the season of birth may play a role in determining the risk of developing certain medical conditions, including autoimmune diseases like Hashimoto’s thyroiditis.

Hashimoto’s thyroiditis is an autoimmune disorder that affects your thyroid gland. It occurs when the immune system mistakenly attacks the thyroid, leading to hypothyroidism. While the exact cause of this condition is theorized to be a combination of environmental triggers and genetic factors, scientists have been studying the potential influence of birth season on its development.

Understanding the influence of birth season on the risk of autoimmune disease and Hashimoto’s thyroiditis is important, as it can provide valuable insights into the underlying mechanisms of the disease. In this article, we will explore the relationship between your birth season and autoimmune disease risk, with a particular focus on Hashimoto’s thyroiditis.

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There is an increasing body of evidence to suggest that the season of birth may be related to the risk of developing various health conditions, some of which include:

• Atherothrombosis (plaque, clots, and vascular disease)
• Asthma
• Attention deficit hyperactivity disorder (ADHD)
• Autoimmune disease
• Bipolar disorder
• Congestive heart failure
• Developmental dyslexia
• Heart disease
• Multiple sclerosis
• Schizophrenia
• Sleep disorders
• Type 1 diabetes

In fact, researchers at Columbia University found that 55 out of 1,688 diseases are correlated with the season of birth.

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Researchers have identified several important factors that may explain this birth season-disease link, including: 

Environmental factors: Many environmental factors experienced by a pregnant woman – and her developing baby in utero – appear to influence the disease risk. These environmental factors include sunlight exposure, temperature, humidity, and time spent outdoors, which all vary by season. For example, exposure to antigens like pollen may contribute to specific disease risk.

Nutrient status: Seasonal changes can affect nutrient status, such as fresh fruit and vegetable availability or iodine intake, affecting disease risk.

Prenatal vitamin D synthesis and status: Vitamin D is synthesized in the skin in response to sunlight exposure, and vitamin D status is known to be lower in the winter months. Low vitamin D status has been linked to several diseases, including autoimmune diseases.

Genetic-epigenetic links: There appear to be genetic and epigenetic links between season of birth and disease risk. Some people have a genetic predisposition to developing certain health conditions. This can be passed down via the DNA from your biological parents. For example, a study found that certain genetic variants were associated with the risk of developing multiple sclerosis in individuals born in the spring.

These factors come under an umbrella that’s now referred to as the Fetal Origins of Adult Disease (FOAD) hypothesis. This hypothesis proposes that events experienced in utero have a profound impact on one’s risk for the development of future adult disease. 

Dr. David Barker first popularized the FOAD hypothesis, which has received considerable attention since its inception. The FOAD hypothesis has far-reaching implications, as indicated by the following statement by the World Health Organization, “The global burden of death, disability and loss of human capital as a result of impaired fetal development is huge and affects both developed and developing countries.”

The FOAD hypothesis proposes that although occurring in response to a transient phenomenon (i.e., poor nutrition in utero), these adaptations become permanent or “programmed” alterations in regional blood flows and organ growth when nutrient or oxygen supply is reduced.

The provision of nourishment during fetal development depends on the maternal diet, the placenta’s ability to supply nutrients (amino acids, glucose, fat, oxygen, and growth-stimulating hormones), and the mother’s own in-utero experience. In other words, the effect of FOAD extends beyond the first generation. The FOAD hypothesis has far-reaching implications and includes babies exposed to nutritional and non-nutritional stress during different critical periods of development, which ultimately result in a disease state.

The FOAD hypothesis also suggests that some common degenerative diseases could even be prevented by improving maternal health and fetal nutrition. As a result, healthcare professionals and policymakers are increasingly prioritizing this issue so they can eventually implement preventive measures and treatment for those at higher risk for chronic diseases.

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Autoimmune diseases are a group of disorders in which the immune system mistakenly attacks the body’s tissues. There is growing evidence that the season or month of birth may be associated with the risk of developing autoimmune diseases later in life. Here is what the research says about the relationship between season or month of birth and the risk of autoimmune disease.

A study published in the Journal of Clinical Endocrinology and Metabolism found that individuals born in winter months had an increased risk of developing autoimmune Addison’s disease (AAD). The study analyzed data from 1,484 patients with AAD and 4,584 controls and found that the risk of developing AAD was 30% higher for those born in December through February compared to those born in June through August.

Another study published in BMC Medicine found a season of birth effect in autoimmune diseases such as multiple sclerosis (MS) and type 1 diabetes (T1D). The study analyzed data from 115,172 patients with immune disorders and found that the birth distribution of patients with autoimmune diseases followed a seasonal distribution compared to the general population. The study also found that being born in the spring or summer months increased the risk of developing MS and T1D.

A systematic review published in the journal Endocrinología, Diabetes y Nutrición analyzed 11 studies that investigated the seasonality of the month of birth in patients with autoimmune endocrine diseases. The review found that 73% of the studies found a seasonal pattern, and 64% showed birth peaks in spring and/or summer. The review also found that Hashimoto’s thyroiditis exhibited a higher seasonality in women. 

A study published in the journal Multiple Sclerosis and Related Disorders found that the month of birth was associated with MS development primarily among men with a higher risk if born in the early fall months (September and October).

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Research exploring the potential association link between Hashimoto’s thyroiditis and birth season has suggested some interesting correlations. One major systematic review of 11 separate studies found that individuals born in the spring or summer – specifically, June – had a higher risk of developing Hashimoto’s thyroiditis compared to those born in the fall or winter. The study analyzed data from 1,731 patients with autoimmune thyroid disease and 17,310 controls and found that individuals with Hashimoto’s had a significantly increased risk of being born in June and between June and August.  

A review published in the journal Endocrinology and Metabolism analyzed the clinical relevance of environmental factors in the pathogenesis of autoimmune thyroid disease. The review found that the season of birth was one of the environmental factors that could influence the development of autoimmune thyroid disease. 

So, what could be the reason behind this seasonal influence on the risk of Hashimoto’s thyroiditis? 

It’s clear that vitamin D levels may play a role. It is well-known that vitamin D deficiency is more common during the winter months due to decreased sun exposure. Vitamin D is crucial for maintaining a healthy immune system, and its deficiency has been linked to various autoimmune diseases, including Hashimoto’s thyroiditis. Therefore, it is possible that lower vitamin D levels during winter gestation could increase the risk of Hashimoto’s in the baby after birth.

Another theory suggests that seasonal fluctuations in environmental factors, such as viral infections, may trigger the development of Hashimoto’s thyroiditis in susceptible individuals. It is thought that certain viral infections during early life could contribute to the dysregulation of the immune system and increase the risk of autoimmune diseases, including Hashimoto’s thyroiditis. Therefore, exposure to specific infections during different seasons might explain the higher risk observed in individuals born in the spring and summer.

Despite these intriguing findings, birth season is just one of many factors that can influence the risk of Hashimoto’s thyroiditis. Genetic predisposition, gender (as it is more common in women), and environmental factors such as stress and exposure to certain chemicals and pollutants also play a significant role in developing this condition.

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The research suggests a relationship between the season or month of birth and the risk of autoimmune disease, including Hashimoto’s thyroiditis. More research is still needed, however, to understand the mechanisms underlying this relationship fully and whether this understanding can help with disease prevention or treatment. 

Meanwhile, no matter what time of year you were born, when you have Hashimoto’s and hypothyroidism, you deserve comprehensive, patient-oriented thyroid care. A Paloma Health membership offers many benefits, making it your go-to medical practice for hypothyroidism care. You’ll have convenient virtual access to expert practitioners specializing in thyroid disorders, eliminating the need for in-person appointments and long wait times. All your high-quality care – including complete thyroid blood test panels – is available from the comfort of your own home. Paloma Health also provides comprehensive educational resources, empowering you with knowledge about your condition and promoting better self-management. 

Free T3

Free T3 is a hormone produced by the thyroid gland. Levels of this fluctuate when individuals have an under or overactive thyroid gland.

TSH

Thyroid-stimulating hormone, TSH, is the hormone responsible for controlling hormone production by the thyroid gland. The hormone TSH is considered the most sensitive marker for screening for thyroid diseases and conditions. Our thyroid panel is ideal for TSH testing at home and will tell you how your levels compare to normal TSH levels.

TPO Antibodies

Thyroid peroxidase antibodies are antibodies that can bind to thyroid enzymes, suppressing thyroid function. They are elevated in a condition called Hashimoto's disease, which is the most common type of hypothyroidism in the USA.

Free T4

Free T4 is the predominant hormone produced by the thyroid gland. Levels fluctuate when individuals have an under or overactive thyroid gland. Testing your free T4 with this thyroid function test lets you see if your thyroid hormone production is at a normal level.

Reverse T3

Add-on

RT3 is a metabolite of T4. Typically, when T4 loses an atom of iodine—a process known as monodeiodination—it becomes (T3), the active thyroid hormone.The body also converts T4 into rT3, which is an inactive form of T3 that is incapable of the metabolic activity that is normally carried out by T3.

Vitamin D

Add-on

Some observational studies have found low blood levels of vitamin D in patients with hypothyroidism and Hashimoto’s as well as hyperthyroidism due to Gravesʼ disease. It is not clear from these studies if low vitamin D is a cause, a consequence or an innocent bystander in the development of these common thyroid conditions.

Frequently asked questions

Does the season you were born in affect your risk of Hashimoto's thyroiditis?

It may. A systematic review of 11 studies covering over 1,700 patients with autoimmune thyroid disease found that people born in spring or summer, especially June, had a significantly higher risk of developing Hashimoto's thyroiditis than those born in fall or winter.

Why would birth season affect autoimmune disease risk?

Researchers point to several possible factors, including seasonal changes in vitamin D levels during pregnancy (vitamin D is important for immune function), seasonal viral infections that may affect immune system development, and other environmental exposures like sunlight, temperature, and nutrient availability that vary throughout the year.

What other autoimmune diseases have been linked to birth season?

Studies have found birth-season associations with several conditions, including autoimmune Addison's disease (higher risk with winter births) and multiple sclerosis and type 1 diabetes (higher risk with spring or summer births). One analysis found that 55 out of 1,688 diseases studied showed some correlation with season of birth.

Does vitamin D play a role in Hashimoto's risk tied to birth season?

It may. Vitamin D is synthesized in the skin from sunlight exposure, and levels are typically lower during winter months. Since vitamin D deficiency has been linked to several autoimmune diseases, including Hashimoto's, lower vitamin D during winter gestation is one theory researchers point to for this seasonal pattern.

Is birth season the main cause of Hashimoto's thyroiditis?

No. Birth season is just one of many contributing factors. Genetic predisposition, being female, and environmental factors such as stress and exposure to certain chemicals and pollutants also play a significant role in the development of Hashimoto's thyroiditis.

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Vedrana Högqvist Tabor, Ph.D., contributed to this article.

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