Low cholesterol means your total cholesterol or LDL (“bad”) cholesterol is below the typical range. While most health messaging focuses on high cholesterol, unusually low levels can sometimes signal an underlying medical condition, a genetic trait, or simply reflect effective treatment with medication. There is no universally agreed-upon number that defines “too low” for total cholesterol or LDL, but total cholesterol below about 120 to 150 mg/dL or LDL below 40 mg/dL is generally considered unusually low and worth investigating.
Why There’s No Official “Too Low” Number
Major cardiology guidelines from the American Heart Association and American College of Cardiology focus almost entirely on upper limits, setting treatment targets to bring cholesterol down. They don’t define a formal lower boundary for total cholesterol or LDL. That’s because, from a heart disease standpoint, lower LDL is consistently better. Genetic studies have identified people who naturally carry LDL levels below 20 mg/dL with no apparent health consequences, and newborns typically have LDL in the 20 to 40 mg/dL range.
The one place where “low” is clearly defined is HDL cholesterol, the protective type. For men, HDL below 40 mg/dL is considered low. For women, the threshold is 50 mg/dL. Low HDL is a risk factor for heart disease regardless of what your other numbers look like.
What Can Cause Naturally Low Cholesterol
If your cholesterol is low and you’re not taking medication to lower it, a handful of medical conditions could be involved. The Cleveland Clinic lists these as recognized causes of low cholesterol:
- Liver disease: the liver produces most of your body’s cholesterol, so damage to it directly reduces output
- Hyperthyroidism: an overactive thyroid speeds up cholesterol metabolism
- Malnutrition or poor nutrient absorption from conditions like Crohn’s disease, celiac disease, or chronic pancreatitis
- Adrenal insufficiency (Addison’s disease)
- Kidney failure
- Cancer
- Chronic infections including sepsis and HIV
- Alcohol use disorder
In many of these situations, low cholesterol is a clue rather than the problem itself. A person with undiagnosed liver disease or an overactive thyroid, for example, will typically have other symptoms that lead to a diagnosis. Low cholesterol on a blood panel can sometimes be the first hint that something else is going on.
How Digestive Problems Lower Cholesterol
Your body recycles cholesterol through bile acids, which are released into your intestines to help digest fat and then reabsorbed back into the bloodstream. Conditions that damage the intestinal lining or cause chronic diarrhea disrupt this recycling loop. The result is that cholesterol gets lost in stool instead of returning to circulation. Research on patients with severe malabsorption consistently shows low plasma cholesterol, even though the liver ramps up cholesterol production to compensate. Crohn’s disease, celiac disease, and chronic pancreatitis all work through this mechanism.
Genetic Causes of Low Cholesterol
Some people are born with genes that keep their cholesterol permanently low. The most well-known inherited form is familial hypobetalipoproteinemia, usually caused by mutations in the APOB gene. This gene controls the production of a protein that packages and transports cholesterol in the blood.
Mild cases often cause no symptoms at all. People may go their entire lives with low cholesterol and never know they carry the mutation. More severe cases, however, can lead to fatty liver disease (because fat accumulates in the liver instead of entering the bloodstream normally), difficulty absorbing dietary fats, and deficiencies in fat-soluble vitamins like A and E. In children with severe forms, this can show up as poor weight gain and fatty stools. In some cases, fatty liver can progress to cirrhosis over time.
Low Cholesterol and Cancer Risk
You may have seen headlines linking low cholesterol to cancer. The association is real in observational data, but the explanation matters: it’s likely reverse causation. Undiagnosed cancers alter the body’s metabolism and pull cholesterol levels down before a tumor is ever detected. Cholesterol levels tend to decline in the years leading up to a cancer diagnosis, and when researchers exclude the first few years of follow-up data from large studies, the link between low cholesterol and cancer weakens significantly. In other words, it’s not that low cholesterol causes cancer. It’s that early-stage cancer causes low cholesterol.
Does Very Low LDL Raise Stroke Risk?
A longstanding concern has been that very low LDL might weaken blood vessel walls and increase the risk of bleeding strokes (hemorrhagic strokes). Recent evidence has largely put this worry to rest. A study published in the AHA journal Circulation examined patients with prior strokes who achieved very low LDL levels through medication and found hemorrhagic strokes were infrequent and completely unrelated to how low LDL went. There was no trend toward more bleeding events at lower levels. This aligns with findings from other large trials using different cholesterol-lowering drugs.
Low Cholesterol From Statins or Other Medications
If your cholesterol is low because you’re taking a statin or another lipid-lowering medication, the current evidence is reassuring. Long-term follow-up data from major clinical trials shows no safety concerns even when LDL drops below 20 mg/dL through treatment. Safety outcomes at these very low levels were statistically identical to outcomes at higher levels. Based on this, cardiology guidelines now state there is no reason to reduce or modify therapy just because LDL has dropped very low. For people being treated to prevent a second heart attack or stroke, pushing LDL as low as possible appears to provide continued benefit without a safety tradeoff.
Low Cholesterol During Pregnancy
Pregnancy is one situation where very low cholesterol raises specific concerns. Cholesterol plays a role in fetal development, and research from the National Human Genome Research Institute found that pregnant women with total cholesterol below 159 mg/dL faced a notably higher risk of premature birth. Among white women in the study, 21 percent of those with the lowest cholesterol levels delivered before 37 weeks, compared to about 5 percent of women with moderate cholesterol (159 to 261 mg/dL). Full-term babies born to mothers with low cholesterol also weighed about 5 ounces less on average, and researchers observed a trend toward smaller head sizes. The low cholesterol in these women was related to genetics, diet, or other health factors rather than medication.
When Low Cholesterol Needs Attention
For most people, low total cholesterol or low LDL on a blood test is not a problem in itself. If you’re taking medication to lower cholesterol and your numbers are very low, that’s generally working as intended. If your cholesterol is unexpectedly low without medication, it’s worth a conversation with your doctor to check for underlying conditions, particularly liver or thyroid problems, digestive disorders, or nutritional deficiencies. A single low reading on a routine panel doesn’t necessarily mean something is wrong, but a pattern of declining cholesterol over time, or very low cholesterol paired with symptoms like fatigue, unexplained weight loss, or digestive issues, deserves further workup.