Hypothyroidism affects approximately 5 percent of persons in the United States older than 12, as noted in December 2012 medical practice guidelines published in the journal Thyroid. Hypothyroidism affects women more frequently than men and the likelihood of developing the condition increases with age.
Because thyroid hormones influence the activity of virtually all body tissues, hypothyroidism can cause a wide array of diverse symptoms. Water weight gain and bloating are two possible symptoms that can occur for several reasons, alone or in combination.
Slow Stomach Emptying
Your digestive organs propel food through the gastrointestinal system via coordinated, involuntary rhythmic contractions. Hypothyroidism slows this propulsion, known as peristalsis.
One of the effects of this slowing is delayed stomach emptying, meaning it takes longer for food and beverages to pass from the stomach to the small intestine after eating. This delay can contribute to a sensation of abdominal bloating, particularly after meals.
The slowed peristalsis that occurs with hypothyroidism also affects the intestines. The prolonged time it takes for food and waste to move through the intestines frequently leads to constipation, a common symptom in people with hypothyroidism. The accumulation of stool in the colon caused by constipation is often accompanied by a sense of fullness and bloating of the abdomen.
Salt and Water Retention
Hypothyroidism affects the kidneys in several ways, all of which contribute to salt and water retention with water weight gain. The blood filtering function of the kidneys decreases in people with low thyroid hormone levels, leading to a reduced ability to get rid of excess body water via the urine.
Additionally, hypothyroidism causes changes in hormone levels that provoke increased salt and water retention by the kidneys, further contributing to water weight gain. Finally, people with hypothyroidism appear to be more sensitive to dietary salt, as reported in an October 2011 review article published in the Indian Journal of Endocrinology and Metabolism.
Low thyroid hormone levels sometimes cause changes in the skin that lead to swelling, or edema. Edema caused by hypothyroidism is called myxedema or thyroid dermopathy. The fluid accumulation in the skin is thought to occur because of increased amounts of a chemical called hyaluronic acid.
This chemical pulls water into the skin, increasing its thickness and causing it to feel doughy. While the skin all over the body is typically affected, myxedema is often most noticeable in the face and hands. Thyroid dermopathy usually occurs only in people with severe hypothyroidism but can contribute to overall water weight gain.
Other Considerations and Next Steps
Thyroid hormone replacement medication is highly effective in reversing the symptoms of hypothyroidism. According to the American Thyroid Association, weight gain associated with hypothyroidism is typically about 5 to 10 pounds — most of which is water weight. This weight is usually lost with thyroid hormone replacement therapy.
See your doctor if you experience any signs or symptoms that might signal hypothyroidism. In addition to weight gain and bloating, these could include:
- Feeling cold
- Fatigue and/or weakness
- Muscle and/or joint achiness
- Forgetfulness and/or difficulty concentrating
- Hair loss or thinning
- Dry skin
- Irregular menstrual periods
- Thyroid: Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association
- American Family Physician: Hypothyroidism: An Update
- Cleveland Clinic Center for Continuing Education: Hypothyroidism and Hyperthyroidism
- Dermatoendocrinology: Thyroid Hormone Action on Skin
- Indian Journal of Endocrinology and Metabolism: The Thyroid Hormone, Parathyroid Hormone and Vitamin D Associated Hypertension
- European Journal of Endocrinology: Management of Endocrine Disease: Hypothyroidism-Associated Hyponatremia: Mechanisms, Implications and Treatment
- Journal of Clinical Endocrinology and Metabolism: Association between Hypothyroidism and Small Intestinal Bacterial Overgrowth
- Gastroenterology Research and Practice: Does Hypothyroidism Affect Gastrointestinal Motility?
- American Thyroid Association: Thyroid and Weight
- MyThyroid.com: Hypothyroidism; Daniel J. Drucker, MD