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How Does Thyroid Hormone Affect Cholesterol, LDL, and the Triglycerides?

Published December 7 2015

Having a thyroid hormone imbalance will have an effect on the lipids, which in turn can usually be seen on a lipid panel.  As a result, balancing the thyroid hormone levels will almost always cause positive changes on a lipid panel, although there are times when other factors can lead to these deviations.  What I plan on doing in this blog post is to talk about the impact of thyroid hormone on the total cholesterol, LDL, and some of the other basic lipid markers.  I’m not going to discuss the effect of thyroid hormone on other lipid markers such as LDL particles and lipoprotein a, but I probably will write a future article that talks about these markers.

Before talking about some of the individual markers on a lipid panel, I’d like to briefly explain how thyroid hormones affect lipid metabolism.  An enzyme called 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is important for the synthesis of cholesterol.  In fact, when someone is given a statin to lower their cholesterol, these drugs inhibit this enzyme.  Thyroid hormone plays an important role in regulating HMG-CoA reductase, and it also affects the metabolism of LDL and HDL.

Total cholesterol.  While many medical doctors still recommend statins on a frequent basis to lower total cholesterol, it’s important to understand that having very low cholesterol levels also isn’t a good thing.  First of all, cholesterol is an important component of cell membranes, and therefore is present in every cell in the body.  Cholesterol helps to maintain the integrity and fluidity of the cell membrane.  Cholesterol is also an important precursor for the steroid hormones, as well as for the synthesis of vitamin D.  In other words, without cholesterol your body wouldn’t be able to produce progesterone, estrogen, testosterone, cortisol, and all of the other steroid hormones.  Nor would it be able to produce vitamin D.  Cholesterol is also converted into bile in the liver, which in turn is necessary for the absorption of fats.  So while you don’t want cholesterol to be too high, you also don’t want it to be too low.

A condition such as hypothyroidism is of course characterized by low thyroid hormone levels, and even though a decrease in thyroid function actually leads to a reduction in the activity of HMG-CoA reductase, both total cholesterol and LDL-C levels are usually increased in patients with hypothyroidism (1) [1] (2) [2] (3) [3].  This is due to the decreased LDL-receptors’ activity, resulting in decreased breakdown of LDL (4) [4] (5) [5].  This is why people with hypothyroidism and Hashimoto’s Thyroiditis will commonly have an elevated total cholesterol on a lipid panel, and increasing the thyroid hormone levels will help to decrease the total cholesterol, along with the LDL.  On the other hand, those with hyperthyroidism and Graves’ Disease usually have a normal or lower total cholesterol and LDL (6) [6], although being on antithyroid medication such as Methimazole or PTU can make the person temporarily hypothyroid, and thus cause an elevation in the total cholesterol and/or LDL.

Low density lipoprotein (LDL).  As the name implies, a “lipoprotein” consists of both lipids and proteins.  Lipoproteins transport fats such as cholesterol, phospholipids, and triglycerides around the body.  Although LDLs aren’t a type of cholesterol, they are frequently labeled as being a “bad” cholesterol because they transport fat to the artery walls which in turn can lead to atherosclerosis.  As I mentioned earlier, hypothyroidism usually causes an increase in LDL-C levels due to a decrease in LDL-receptor activity, which results in a decrease in the breakdown of LDL.  On the other hand, LDL levels are usually normal or on the lower side in hyperthyroidism and Graves’ Disease.

High density lipoprotein (HDL).  HDL carries cholesterol and other fats away from the artery walls and to the liver, and because higher levels of HDL is associated with a decreased risk of atherosclerosis it is known as the “good cholesterol”.  In hypothyroidism, HDL levels are usually normal, or elevated in severe cases, whereas in hyperthyroidism the HDL levels are usually either normal or decreased (7) [7] (8) [8].  As for why HDL frequently increases in severe cases of hypothyroidism, it is due to decreased activity of something called cholesteryl-ester transfer protein (CETP) and hepatic lipase, which are enzymes regulated by thyroid hormones (8) [8]. The low activity of these enzymes during severe cases of hypothyroidism is what leads to the increase in HDL.

Triglycerides.  Triglycerides are blood lipids derived from glycerol and three fatty acids.  Triglycerides are obtained through the diet, although the liver also synthesizes triglycerides.  While cholesterol levels remain fairly constant when tested throughout the blood, triglyceride levels can fluctuate considerably from day to day, and are at the highest one to four hours after meals (9) [9].  Collection of blood for triglyceride testing should be done after a 12-hour fasting period (9) [9].  Triglycerides are usually normal or elevated in people with hypothyroidism, and are usually normal in those with hyperthyroidism.  One small study looked at the metabolism of triglycerides in those with hypothyroidism and hyperthyroidism, and it showed that nonobese hypothyroid patients and those with hyperthyroidism generally had normal levels of triglycerides, whereas obese patients with hypothyroidism often had elevated levels of triglycerides (10) [10].

Although hypothyroidism can cause elevated triglyceride levels, eating too many carbohydrates can also cause this to increase (11) [11], and it is common to see high triglyceride levels in people with insulin resistance and type 2 diabetes (12) [12] (13) [13].  Although I don’t get too concerned when I see mildly elevated levels of cholesterol, I don’t like to see the triglycerides too high on a blood test.  In fact, while triglycerides are considered to be normal if they’re less than 150 mg/dL, it is best to keep the triglycerides less than 100 mg/dL.

Very low density lipoprotein (VLDL).  This is yet another type of lipoprotein made by the liver, and these transport fats and cholesterol into the bloodstream.  When compared to the other types of lipoproteins, VLDLs contain the highest amount of triglycerides, and it is considered to be a “bad” type of cholesterol.  Just as is the case with triglycerides, VLDLs are usually normal or high in those with hypothyroidism, and are usually normal in those with hyperthyroidism (14) [14] (15) [15].  VLDLs are also commonly high in those people with insulin resistance and type 2 diabetes.

How To Have A Healthy Lipid Panel

So if someone has elevated lipid markers, then what should they do in order to normalize them?  Here are a few things that can help:

Balance the thyroid hormones.  While people with hyperthyroidism and Graves’ Disease of course want to have normal thyroid hormone levels, with regards to the lipid panel, people with hypothyroidism and Hashimoto’s have a greater likelihood of having values on a lipid panel that are out of range.  As I mentioned in this article, someone with low or depressed thyroid hormone levels are likely to have an elevated total cholesterol, LDL, and VLDL, and if they are overweight or obese they are likely to have elevated triglycerides as well.  Increasing the thyroid hormone levels will usually help to decrease these elevated values, although in the case of triglycerides, dietary factors will most likely play a greater role in decreasing this value.

Minimize your carbohydrate consumption.  Dietary factors have a greater impact on the triglycerides than on the other markers.  If you have elevated triglycerides then there is a good chance you are eating too many carbohydrates (16) (17) [16].  Obviously you want to eat a healthy diet which consists of whole foods, while minimizing the refined foods and sugars.  If you do this then you are likely to not overdo it when it comes to eating carbohydrates.  However, I’ve seen some people eat a pretty healthy diet, but eat a lot of fruit and/or a lot of gluten free grains.  For most of my patients I recommend for them to not consume more than 200 grams of carbohydrates per day, but if someone has elevated triglycerides it probably is best to consume less than 150 grams of carbohydrates per day, and perhaps even less than 100 grams of carbohydrates, depending on how high the triglycerides are.

Exercise regularly.  Doing aerobic exercise can decrease the triglycerides (18) [17] (19) [18], although for optimal results it’s best to combine this with dietary changes.

Eat plenty of Fiber.  In most cases, high total cholesterol levels aren’t strongly related to one’s diet.  However, there are exceptions, and eating a fiber-rich diet can help to lower cholesterol levels, as numerous studies show that soluble fiber can reduce total cholesterol and LDL levels (20) [19] (21) [20] (22) [21].  The favorable fat composition and fiber contribute to the hypocholesterolemic benefit of almond consumption (23) [22], and numerous studies show that eating almonds can reduce LDL and increase HDL (24) [23] (25) [24].

Certain Supplements Can Help.  There are some supplements which can help lower lipid levels.  Most of the ones I list below help with the lowering of cholesterol and LDL levels.  Some of these can also help to lower triglycerides, although  the best way to accomplish this is usually through dietary changes.  With regards to the supplements that can help decrease total cholesterol and LDL, keep in mind that if you have a thyroid hormone imbalance that is affecting the these lipid markers then this imbalance needs to be addressed.

Garlic.  There are numerous studies which show that taking garlic can help lower cholesterol levels.  One study on rats showed that raw garlic had a profound effect in reducing the glucose, cholesterol, and triglyceride levels, whereas boiled garlic had little effect (26) [25].  A meta-analysis showed that taking one half to one clove per day of garlic resulted in a significant reduction in total cholesterol levels in those with levels greater than 200 mg/dL (27) [26].  Another systematic review showed that garlic reduces total cholesterol to a modest extent, along with triglycerides, but doesn’t lower LDL or increase HDL levels (28) [27].  One study showed that garlic powder and aged garlic extract were more effective in reducing serum total cholesterol levels, while garlic oil was more effective in lowering serum triglyceride levels (29) [28].

CoQ10.  There seems to be little doubt that taking statins will result in low CoQ10 levels (30) [29] (31) [30] (32) [31].  Although CoQ10 is included in some supplement formulations designed to lower cholesterol levels, there isn’t too much evidence that taking CoQ10 lowers total cholesterol or LDL levels.  One study did show that CoQ10 can play a role in preventing and treating atherosclerosis (33) [32].  Another small study showed that CoQ10 supplementation at a dose of 300 mg/day significantly increased antioxidant enzymes activities and reduced the levels of inflammatory markers in people taking statins (34) [33].  But more research needs to be conducted specifically with regards to the effects CoQ10 has on total cholesterol.  There does seem to be more evidence that CoQ10 can help to lower blood pressure (35) [34] (36) [35] (37) [36].

Niacin.  Niacin has been shown to reduce triglycerides, LDL, and VLDL mainly through: a) decreasing fatty acid mobilization from adipose tissue triglyceride stores, and b) inhibiting hepatocyte diacylglycerol acyltransferase and triglyceride synthesis leading to increased intracellular apo B degradation and subsequent decreased secretion of VLDL and LDL particles. Niacin can also raise HDL levels by decreasing the fractional catabolic rate of HDL-apo AI without affecting the synthetic rates (38) [37].  Another study showed that low dose niacin can be used as an inexpensive agent for elevating HDL levels and altering the total cholesterol/HDL ratio (39) [38].  However, a recent systematic review showed that niacin does reduce cardiovascular disease, although this may occur through a mechanism not reflected by changes in HDL concentration (40) [39].  One thing to keep in mind is that there are different types of niacin, and immediate-release niacin commonly causes flushing, which isn’t harmful, but can be uncomfortable.  And while time-released niacin is usually safe, higher doses can be toxic to the liver.  Just to play it safe it probably is best not to take more than 500 mg/day of niacin on your own.

Red yeast rice.  Many studies show that red yeast rice can lower cholesterol.  One study evaluated the effectiveness and tolerability of red yeast rice to treat dyslipidemia in patients who cannot tolerate statins (41) [40].  The study showed that LDL cholesterol was significantly lower in the red yeast rice group than in the placebo group, and that it also lowered total cholesterol levels (41) [40].  Another study showed that red yeast rice significantly reduces total cholesterol, LDL, and triglycerides (42) [41].  Yet another study looked at the effect of red yeast rice on physicians and their spouses who had a total cholesterol level greater than 200 mg/dL, and the study showed that the red yeast rice was effective in lowering cholesterol and LDL (43) [42].

Plant sterols.  Plant sterols are plant components that have a chemical structure similar to cholesterol except for the addition of an extra methyl or ethyl group (44) [43].  Plant sterols reduce cholesterol absorption and thus reduce circulating levels of cholesterol (44) [43].  In addition to helping to lower total cholesterol, plant sterols can also lower LDL levels (45) [44] (46) [45].

So hopefully you have a better understanding as to how an imbalance in thyroid hormone can affect the lipid markers.  Low thyroid hormone levels commonly cause an increase in total cholesterol and LDL, and it can raise triglycerides as well, especially in overweight or obese individuals.  People with hyperthyroidism and Graves’ Disease will usually have normal or lower lipid levels, although if they are taking antithyroid medication this can cause transient hypothyroidism, thus causing an elevation in these markers.  In order to have a healthy lipid panel you want to balance the thyroid hormone levels, minimize your consumption of carbohydrates, exercise regularly, and eat a diet high in fiber.  Certain supplements can also be beneficial in some cases, such as garlic, CoQ10, niacin, red yeast rice, and plant sterols.