Untreated hypothyroidism can cause high cholesterol levels; low thyroid function slows all of your body's systems. It can cause weight gain, lower your heart rate and make you more sensitive to cold. Once you start to take replacement thyroid hormone, your metabolism and other functions should return to normal. If you have hypothyroidism, your ideal cholesterol levels are the same as someone with normal thyroid function.
Thyroid Function
Your thyroid produces two hormones -- T3 and T4 -- which control the rate your body uses oxygen and energy, otherwise known as your metabolism. Hypothyroidism causes low thyroid hormone production and slows your metabolism. This can lead to weight gain and higher cholesterol levels. Hypothyroidism is simple to treat; levothyroxine is the most commonly prescribed synthetic T4 hormone replacement. Your body can manufacture T3 hormone from T4, even with slow thyroid function. Once you've found your correct dose of levothyroxine, your metabolism will stabilize and everything should return to normal.
Cholesterol
Your body makes cholesterol from dietary fats. You need fat to use for energy and cell production. There are two types of cholesterol. LDL cholesterol, often referred to as the "bad" cholesterol for its ability to build up in your arteries, hardening into plaque and limiting blood flow, raises blood pressure and your risk for cardiovascular disease. HDL cholesterol, the "good" kind of cholesterol, helps to move LDL cholesterol to your liver, where it can be eliminated. The higher your HDL level, the lower your risk of heart disease and stroke.
Cholesterol Percentages
Your total cholesterol level is the sum of your HDL and LDL levels. Anything under 200 mg/dL is considered ideal. But a better indicator of risk is the ratio of LDL to your total cholesterol level. This percentage tells you how much of your cholesterol is good vs. bad. According to the Mayo Clinic, to find your cholesterol ratio, divide your total cholesterol level by your HDL level. A ratio of 4:1 or less is desirable for everyone, whether you have hypothyroidism or not.
Cholesterol and Diet
Follow a cholesterol-lowering diet to help improve your cholesterol and LDL percentages. The American Heart Association suggests choosing low-fat dairy and liquid oils over full-fat dairy and solid fats such as lard and butter. Replace two or more servings of meat with fish or plant-based proteins such as legumes or tofu. Eat leaner meats such as seafood or poultry; remove the skin from your poultry before eating. Substitute egg white for whole eggs. Avoid deep-fried foods -- grill, bake, broil, poach or steam without adding additional fats whenever possible.
