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Vegan Diet May Help Protect Against Hypothyroidism


It has been previously thought that vegans have a greater risk of developing hypothyroidism due to a low intake of the mineral iodine. However, a new study from researchers at Loma Linda University suggests that a plant-based diet may actually be protective.

Hypothyroidism is a state in which thyroid hormone production is below normal. This very common condition, affecting about 3 to 5% of the adult population, is characterized by symptoms such as fatigue, weight gain or difficulty losing weight, constipation, depression, thinning or brittleness of the hair or nails, cold intolerance, memory loss and muscle aches and pains.

Thyroid hormones are produced by the thyroid gland which is located in the lower part of the neck, below the Adam’s apple. The thyroid gland uses iodine to produce hormones such as thyroxine (T4) and triiodothyronine (T3).

Because iodine is a necessary mineral for thyroid hormone production, being deficient can lead to hypothyroidism. Vegetarians and vegans consume less iodine than their omnivorous counterparts, as animal foods are one source of the mineral. But is the lowered consumption too low, leading to disease?

To study this, researchers used data from the Adventist Health Study-2 (AHS-2) in which about 97,000 members of the Seventh-day Adventist church were included. Most members of the church follow a lacto-ovo vegetarian diet (one that allows milk and eggs but not animal flesh.) Studies in the past have suggested that this population has a 50% lower risk of developing heart disease, certain types of cancers, strokes, and diabetes.

A food frequency questionnaire was administered to identify the differing types of vegetarians in the study population, ie vegetarians versus vegans. The amount of salt added to the diet was also in question, as most salt in the US is iodized.

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Overall, vegans diets were most often associated with protection against hypothyroidism. The data was not clear about the use or non-use of salt within these diets, so that does not appear to be a major factor in the results. However, one finding was clear.

Vegans were less likely to be obese. As mentioned earlier, thyroid dysfunction often results in weight gain. Even slight variations in thyroid function have been found to lead to excess weight because fat cells produce compounds that negatively affect energy expenditure. What is not exactly known yet is which comes first – obesity or thyroid dysfunction. A vegan diet may be protective by being lower in calories, resulting in weight loss sufficient to preserve thyroid function.

Another notable benefit to either a vegetarian or vegan diet is the elimination of red meat. Consumption of beef and pork is associated with higher levels of high-sensitivity C-reactive protein (CRP). CRP is a measure of general levels of inflammation in the body. Many thyroid conditions involve inflammation.

This study is a first to evaluate the role of a vegetarian or vegan diet in thyroid dysfunction and there are many unknowns. However, vegan diets that are well-planned (to include all of the necessary components for good health) offer many health benefits, because of its higher content of fiber, folic acid, vitamins C and E, potassium, magnesium and many phytochemicals.

Those who follow plant-based diets typically enjoy a lower risk of cardiovascular disease, type 2 diabetes and some cancers.

Dietary recommendations for an optimal vegan diet include:
• Regular consumption of B-12 fortified foods, such as fortified soy and rice beverages, certain breakfast cereals and meat analogs, and B12 fortified nutritional yeast.
• Ensure adequate calcium by consuming green leafy vegetables, tofu, tahini, and calcium-fortified beverages.
• Especially during the winter, consume foods with vitamin D, such as fortified soy or rice milk, fortified orange juice, breakfast cereals and fortified margarines.
• Consume foods that are naturally rich in the omega-3 fatty acid ALA such as ground flaxseed, walnuts, canola oil, soy products and hemp seed-based beverages.
• Consume foods that contain zinc, such as whole grains, legumes, and soy products.
• For iodine, use iodized salt, breads containing iodine, and seaweeds such as kelp (kombu). However, do not overdo iodine intake – it only takes 100-300 micrograms per day to meet needs for optimal thyroid function.

Journal Reference:
Tonstad S et al. Vegan Diets and Hypothyroidism. Nutrients 2013 5, 4642-4652; doi:10.3390/nu5114642

Additional References:
Bernadette Biondi. Thyroid and Obesity: An Intriguing Relationship. The Journal of Clinical Endocrinology and Metabolism, August 1 2010 vol 95 no 8.
Verma A et al. Hypothyroidism and Obesity. Cause or Effect? Saudi Med Journal 2008 Aug; 29(8):1135-8.
Pearce EN et al. The prevalence of elevated serum C-reactive protein levels in inflammatory and noninflammatory thyroid disease. Thyroid. 2003 Jul;13(7):643-8.
Craig WJ. Health effects of vegan diets. Am J Clin Nutr May 2009 vol 89 no 5 1627S-1633S
The Vegan Society: Iodine