Nutrition, Thyroid and Fertility

Adapted by Melissa Gorley. Originally from Fertility, Cycles and Nutrition by Marilyn Shannon

A number of factors may cause thyroid function to be abnormally low, resulting in either subclinical or full-blown hypothyroidism. Nutritional deficiencies can prevent the thyroid gland from doing its job. Iodine is well known to be essential for the production of thyroid hormones, but a number of other vitamins, minerals, and the essential fatty acids are also necessary for the production and activation of thyroid hormones.

One of the most common causes of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune disease in which one’s own antibodies disrupt normal thyroid function. In some women, the thyroid gland may temporarily malfunction for a time after a woman gives birth, but it often corrects itself within a few months. Sometimes, though, persistent hypothyroidism begins after childbirth. Removal of the thyroid gland due to elevated thyroid function or thyroid cancer also produces hypothyroidism, which must be treated medically. Low thyroid function can occur due to insufficient medical replacement of thyroid hormone, or replacement with T4 alone, instead of a mix of T4 and T3, as is more natural.

Hormones from other glands also affect thyroid function. Normal levels of progesterone from the corpus luteum stimulate the thyroid. Progesterone enables the body’s cells to bind T3, so that the cells can respond to thyroid hormone. Progesterone also decreases the production of a blood protein called thyroxine-binding globulin, an effect that increases the availability of thyroid hormone to the cells. Conversely, high estrogen levels block the function of thyroid hormones within the body cells. The adrenal hormone cortisol, which rises during prolonged stress, also blocks the function of the thyroid hormones within the body’s cells.


Improving the diet generally is helpful to the entire body, and it is basic to glandular health. Ocean fish is one food to emphasize for thyroid function, since it is a source of iodine as well as omega-3 fatty acids. However, when it comes to low thyroid function, certain foods should be avoided or eaten in moderation.


  • Trans fats found in processed foods such as shortening, margarine and fast foods, especially pastries, interfere with normal cellular function and should be avoided by everyone.
  • Unfermented soy foods eaten in significant quantities have anti-thyroid properties that can affect thyroid function. Avoid soy milk, soy powder, tofu, and so forth as part of your self care for low thyroid function. (Intake of foods which contain soy oil, such as salad dressings, need not be restricted.)
  • Very high consumption of certain raw vegetables and fruits can also have anti-thyroid effects. These include cabbage, Brussels sprouts, broccoli, kale, radishes, turnips, spinach, mustard greens, peanuts, peaches, and pears. Please do not avoid these healthy foods entirely; if they are cooked, the potentially anti-thyroid enzymes are destroyed. According to thyroid patient advocate Mary Shomon, people who have had their thyroid gland removed and who are receiving thyroid replacement hormones do not need to be concerned at all, but even those who are dealing with low thyroid function can eat these vegetable and fruits, raw or cooked, in ordinary moderation.
  • Finally, if you are fighting low thyroid function, you may wish to drink purified water. Both fluoridated and chlorinated water can interfere with the thyroid gland’s use of iodine.


Adding iodized salt (not plain sea salt) to the diet has improved cycle irregularity and irregular mucus patterns in women who were using little or no iodized salt. If you prefer not to consume extra salt, you can get iodine from a multivitamin/multimineral or from tablets of kelp, a type of seaweed (150–225 mcg of iodine is a typical daily dose).


Nutrition and other self care by themselves can improve the symptoms listed above. However, in some cases thyroid hormone replacement may be necessary. If so, you should be aware that there are more and more doctors who are willing to prescribe natural thyroid replacement, because it contains the active T3 form as well as the less active T4 hormone.