Nothing will change your genetic risks, but at least you can avoid making them worse.
Make sure you get enough iodine.
This mineral is essential for the production of thyroid hormones. Years ago, before iodine was added to salt, flour, water, animal feed, and milk, iodine deficiency was rampant. Today, it’s rare in America, though strict vegans can be at risk if they eliminate all eggs and dairy, as can the elderly if they avoid iodized salt to lower their blood pressure. Note: The salt in processed foods (the source of most sodium in our diets) is generally not iodine fortified. Take a multi that contains the mineral.

Limit soy products
Soy isoflavones can suppress thyroid function if you eat too much. Menopausal women who take large amounts to ease symptoms are most at risk.

Stay clear of thyroid supplements with seaweed extracts or the thyroids of desiccated pigs. They’re sold over-the-counter but they are unregulated, so you have no reliable way of knowing how much of the active ingredients you are actually taking.

Be sure your neck is covered when you have a mammogram or dental x-rays. Although the risks are very slight, this low-dose radiation may contribute to thyroid cancer.

Quit smoking
It doesn’t cause hypothyroidism, but it can increase the severity and effects.
Source: Prevention Magazine January 2012