HDL (high-density lipoprotein) is often referred to as the “good” cholesterol because it helps to remove the “bad” cholesterol from the body and is required for many vital processes within the body. Having high levels of HDL cholesterol has been shown to decrease your risk for heart disease. Read on to learn how to increase HDL levels with simple lifestyle and dietary modifications.
What is HDL Cholesterol?
HDL-cholesterol is cholesterol bound to high-density lipoprotein (HDL) particles, which are made in the liver and consist of proteins and fats (lipids). They are called high-density because they contain the highest proportion of protein to lipids, making them denser than other types of lipoprotein particles such as LDL [1].
HDL particles help remove excess cholesterol from the blood by [2, 3, 4]:
- transporting it to the liver, where it becomes a part of bile and is excreted through feces
- taking it to adrenal glands, ovaries, and testes, where cholesterol is converted into steroid hormones (e.g. cortisol, estrogens, testosterone)
Cholesterol transported by HDL is known as “good” cholesterol because it is being removed from artery walls, which helps prevent, reduce, and even reverse hardening of the arteries (atherosclerosis) and heart disease [2].
HDL also plays a role in reducing oxidative stress and inflammation, improving cell and immune function, enhancing insulin sensitivity, and may protect against neurodegenerative disorders [5, 6, 7].
HDL-C Blood Test
An HDL-cholesterol test is a routine blood test that can help your doctor estimate your risk of heart disease.
More recently, scientists have discovered that HDL is made up of particles of different sizes. Having higher levels of large HDL particles is strongly associated with a lower risk for heart disease while having higher levels of small HDL particles is less protective. There are blood tests available today that can determine the sizes that make up the HDL cholesterol in your body. These tests are more expensive and they are used less often than the HDL-C test [8, 9].
HDL-C Normal Range
HDL-C levels can be classified as follows [10, 11]:
- High risk: < 40 mg/dL (1.0 mmol/L) for men or < 50 mg/dL (1.3 mmol/L) for women
- Average risk: 40-50 mg/dL (1.0-1.3 mmol/L) for men and between 50-59 mg/dl (1.3-1.5 mmol/L) for women
- Low risk: > 60 mg/dL (1.55 mmol/L)
High levels of HDL cholesterol has repeatedly been shown to protect against heart disease. Low levels, on the other hand, increase heart disease risk [12, 13].
Causes of Low HDL-C Levels
Causes listed below are commonly associated with low HDL cholesterol. Work with your doctor or another health care professional to get an accurate diagnosis. Your doctor will interpret this test, taking into account your medical history, signs and symptoms, and other test results.
1) Smoking
Cigarette smoking has been undeniably proven to be a preventable risk factor for heart disease. Cigarette smoking is associated with low HDL-C levels and cigarette smoke can directly damage the HDL-C molecule resulting in a dysfunctional HDL-C molecule that has lost its heart-protective properties [14, 15, 16].
2) Lack of Physical Activity
Lack of physical activity decreases HDL-C cholesterol [17].
3) Obesity
Obesity decreases HDL-cholesterol levels [18, 19].
4) Diabetes
Many of those who have type 2 diabetes have a low concentration of HDL-C. HDL particles are also smaller and denser than normal (less protective). Studies suggest there is an increased breakdown of HDL-C in diabetes [17].
5) Overactive Thyroid (Hyperthyroidism)
Thyroid hormones can decrease the production of HDL-C in favor of VLDL-C (bad cholesterol) [20].
6) Liver Disease
Liver disease, such as cirrhosis, can decrease HDL-C levels [21].
7) Infections, Inflammation, and Severe Illness
Inflammatory conditions such as bacterial, viral, and parasitic infections or inflammatory disorders can decrease HDL-C and other types of cholesterol [22, 23].
In addition, severe illness, such as cancer, or injury also decrease cholesterol production [24, 25].
8) Genetic Disorders
Apolipoprotein A1 (ApoA-1) is the main protein in HDL particles. People with mutations in the gene that codes for ApoA-1 have extremely low HDL-C levels and also early onset cardiovascular disease [26].
ATP-binding cassette transporter (ABCA1), also known as the cholesterol efflux regulatory protein (CERP), is a protein that controls the movement of cholesterol throughout the body. Mutations in the ABCA1 gene are found in 5-21.4% of individuals with low HDL cholesterol [26].
Lecithin cholesterol acyltransferase (LCAT) is a protein that plays a role in the formation of lipoproteins such as HDL and LDL. Severe mutations in LCAT cause familial LCAT deficiency (FLD). A 70-80% decrease in HDL-C levels is observed in patients with familial LCAT deficiency. Many studies of various ethnic groups have been conducted and found between 2-25% of people with low HDL-C have a mutation in the LCAT gene [27, 26].
9) Medication
Some drugs can also decrease HDL-C levels, including [28, 29]:
- Anabolic steroids
- Beta-blockers (drugs that lower blood pressure)
- Antipsychotics
10) Aging
Studies have shown that HDL-C cholesterol levels decrease as we age [30].
Increasing HDL-C
If your HDL-C is low, the most important thing is to work with your doctor to find out what’s causing your low HDL cholesterol and to treat any underlying conditions.
The additional lifestyle changes listed below are other things you may want to discuss with your doctor. None of these strategies should ever be done in place of what your doctor recommends or prescribes!
1) Exercise
Exercise increases HDL levels through multiple pathways and recent studies suggest that any type of exercise can be beneficial and the effects will accumulate over time [31, 32, 33, 34].
A study of 18 overweight men and women who went through 12 weeks of regular endurance training found an increase in HDL levels in men and a favorable shift in HDL subfraction in women, without any changes in their diet [35].
Two studies of children found that increasing physical activity increased HDL-cholesterol by lowering body fat [36, 37].
A study (prospective observational) of 200 men found that the increase in HDL with regular endurance training is most significant in those who also have high levels of triglycerides and excessive abdominal fat [38].
2) Quit Smoking
Smoking decreases HDL-C. Studies suggest that HDL-cholesterol improves soon after quitting [17, 15, 16].
3) Lose Weight
Many studies have shown that losing weight, regardless of which diet you follow, can result in a sustained increase in HDL cholesterol. A cohort study of 3,480 Japanese adults found that losing at least 3 kg (6.6 lbs) resulted in an average of 4 mg/dL increase in HDL cholesterol [39, 40, 41, 42, 43, 44].
4) Switch to a Healthy, Balanced Diet
A good example of a diet that can improve HDL-cholesterol and help decrease the risk of heart disease is the Mediterranean diet, which is rich in fruits and vegetables, whole grains, legumes, nuts, herbs, and spices. It is also high in monounsaturated fats found in olive oil [45, 46].
Fruits, Vegetables, and Fiber
Studies suggest that fiber, found in fruits and vegetables, is beneficial in general, while eating processed carbs can have a negative effect on HDL-cholesterol [47, 48].
Olive Oil
Saturated fat, found in dairy and fatty cuts of meat, increases both LDL and HDL. Replacing saturated fat with “healthy fats” (polyunsaturated or monounsaturated fat found in nuts, seeds, avocados, vegetable oils) has been shown to lower both LDL and HDL cholesterol [49].
Numerous studies have shown that supplementing your diet with olive oil can help lower total cholesterol and raise HDL cholesterol. Olive oil contains antioxidants called polyphenols that are responsible for its heart-protective properties [50, 51, 52, 53].
Olive oil also improves cholesterol profiles by improving HDL’s ability to mediate proper cholesterol transport. A study in 26 healthy human volunteers suggests that olive oil (25 mL/day) improves cholesterol profiles by increasing the production of the proteins ABCA1 and ABCG1 which transport fats across cell membranes [54, 55, 56, 57].
Olive oil also helps to increase the anti-inflammatory properties of HDL. A study performed in 20 healthy adults consuming extra virgin olive oil (25 mL/day) for 12 weeks had increased levels of a protein associated with HDL (paraoxonase 1, PON1) that helps to mediate HDL’s anti-inflammatory properties [58].
Nuts
Several studies have found that adding nuts to the diet, including hazelnuts, almonds, pistachios, cashews, walnuts, and macadamia nuts, can have a beneficial effect on HDL-cholesterol levels [59, 60, 61, 62, 63, 64, 65, 66, 67].
5) Alcohol in Moderation
Studies report that drinking alcohol in moderation (1 drink per day) can increase HDL-cholesterol, but it’s controversial as to whether this is beneficial. Most physicians don’t recommend alcohol as a means to increase HDL-C cholesterol [68, 69, 70].
A link between light to moderate alcohol consumption (1 drink/day for women and 1-2 drinks/day for men) and lower risk of heart disease has been observed in several studies. However, heavy alcohol consumption is not only associated with increased risk for heart disease but also increases your risk for many other diseases such as diabetes or stroke [71, 72].
A study of 2473 men and 1530 women found that participants that reported alcohol intake had higher levels of HDL cholesterol [73].
Another study found moderate alcohol consumption was associated with increased HDL cholesterol levels. The type of alcohol consumed did not affect the increase in HDL and there was no association found between dietary fat and HDL cholesterol levels [74].
6) Supplements
Discuss the following foods and supplements with your doctor. Research has shown they may help increase ”good” cholesterol:
- Berberine [75, 76, 77]
- Cocoa [78, 79, 80]
- Avocado [81]
- Niacin (vitamin B3) [82, 83]
- Sage leaf extract [84, 85]
- Blackcurrant oil [86]
Remember, always speak to your doctor before taking any supplements, because they may interfere with your health condition or your treatment/medications!
Health Effects of Abnormal HDL Levels
The largest risk of low HDL cholesterol is developing heart disease. There is a large body of data suggesting that HDL cholesterol has a heart-protective effect and up to 1/3 of patients with heart disease have “normal” total cholesterol but low HDL levels, highlighting the important role this molecule plays in protecting the heart [13, 87, 88].
HDL also plays an important role in immune function. A large prospective population study of 20,000 adults found that participants with very low HDL had a 75% higher risk of infection. Interestingly, very high levels of HDL can also be problematic, as those with very high HDL cholesterol had a 43% higher risk for infectious disease than those with “normal” levels. Very high HDL may be correlated with heart disease as well [89, 90, 6].
Genetics
People with mutations in the following genes have lower levels of HDL cholesterol and are at higher risk for cardiovascular disease [26, 27]:
- APOA1 – the gene that codes for the main protein component in HDL particles
- ABCA1 – the gene that codes for cholesterol efflux regulatory protein
- LCAT – the gene that codes for the protein lecithin cholesterol acyltransferase that regulates the formation of HDL
Limitations and Caveats
A major issue with interpreting the results of studies on HDL is that it’s hard to determine how large a role other factors might play. For example, if there is an association between young males that eat low-fat diets and also have high HDL cholesterol, it’s also possible that those same men are non-smokers who exercise regularly. Additionally, many of these studies are self-reporting and participants do not always respond truthfully [91].
It’s commonly assumed that increasing dietary cholesterol will consequently raise blood cholesterol levels and over time, lead to heart disease. While this is partially true, it’s important to note that only 25% of blood cholesterol is from the diet. The other 75% of cholesterol found in the blood is synthesized by the body, and this is controlled by genetics and affected by other non-dietary environmental factors [92, 93].
