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Blood glucose

How much glucose, or blood sugar, is floating around in your blood. Fasting blood glucose is measured when your stomach is empty (usually before breakfast), whereas postprandial blood glucose is checked after a meal. Both are used as indicators of diabetes risk.

Our evidence-based analysis on blood glucose features 19 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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Summary of Blood glucose

Overview | How are blood glucose levels assessed? | What affects blood glucose?

Overview

Your body breaks down every carb you ingest into glucose, also known as blood sugar because it travels through your bloodstream.[1] Glucose is a simple sugar — more precisely, a monosaccharide (mono meaning single and saccharide meaning sugar). To store glucose, your body combines the molecules into a polysaccharide (poly meaning several) called glycogen, which gets stored in your liver and muscles.

Insulin (a hormone produced by your pancreas) rises when blood glucose rises;[2] it lowers blood sugar by telling various cells to absorb it — for storage in your liver or muscles or for immediate use — and your liver to stop producing new glucose.[3]

The ability of cells to absorb glucose in response to insulin is called insulin sensitivity, and low insulin sensitivity is called insulin resistance. The more sensitive you are to insulin, the less resistant, and vice versa.

It is also possible to produce too little insulin. If you have type 1 diabetes or are in the late stages of type 2 diabetes, in which case you suffer from insulin deficiency, glucose can’t be removed efficiently from your blood, causing hyperglycemia (overly high glucose levels).[4]

Insulin resistance paves the way for type 2 diabetes, which can cause your blood sugar levels to consistently remain too high for too long. If not managed, these high blood sugar levels can lead to serious health complications — mostly cardiovascular diseases,[5] but probably cancer, Alzheimer’s, and Parkinson’s as well.[6][7][8]

How are blood glucose levels assessed?

Glycemic control can be tested several ways, each with its own cutoff values indicating impaired glucose regulation.[9] Of these tests, fasting blood glucose is the most common, followed by hemoglobin A1C (HbA1c).

Methods of glycemic-control measurement

Fasting Plasma Glucose

Fasting plasma glucose (FPG), also known as fasting blood glucose, is simply a measure of how much glucose is floating around in your blood during a fast. After at least 8 hours of not eating (typically in the morning, before breakfast), blood is drawn and analyzed for glucose concentration.

Interpreting FPG results
CONDITIONMILLIGRAMS PER DECILITER
(mg/dL)
MILLIMOLES PER LITER
(mmol/L)

Normal

<100

<5.6

Prediabetic

100–125

5.6–7.0

Diabetic

>125

>7.0

Hemoglobin A1c

Hemoglobin A1c (HbA1c), or glycated hemoglobin, is a marker of blood-glucose metabolism that estimates the average amount of glucose in your blood over the past 3 months.

Interpreting HbA1c results
CONDITION%

Normal

<5.7

Prediabetic

5.7–6.4

Diabetic

≥6.5

The protein that carries oxygen throughout your body, called hemoglobin, is in red blood cells, which live for about 4 months. Glycation is when a sugar — in this case, glucose — is linked to a protein or lipid — in this case, hemoglobin. When blood glucose levels rise, the rate of hemoglobin glycation increases, making glycated hemoglobin an estimate of blood glucose levels over months.

Acute glycemia

There are two types of acute glycemia tests, the more common being the oral glucose tolerance test (OGTT). It involves consuming a specially formulated drink that typically contains 75 grams of glucose and then measuring blood glucose levels at regular intervals over 2 hours. The last blood sample taken is the one used to diagnose.

Interpreting OGTT 2-hour results
CONDITIONmg/dLmmol/L

Normal

<140

<7.8

Prediabetic

140–199

7.8–11.0

Diabetic

≥200

>11.0

In short, the OGTT measures your ability to clear a whole lot of glucose from your bloodstream. It has the advantage of being standardized and easy to administer, but it doesn't accurately reflect the body's response to typical individual mixed-macronutrient meals, which vary by meal and by day.

The other type of acute glycemia test is a postprandial test, which uses real food. The exact same meal is eaten before each measurement. This test is often used to test pharmaceuticals and supplements that may work by reducing the glycemic index (GI) of a meal. The lower the GI, the less it raises your blood glucose.

Random Plasma Glucose Test

For the random plasma glucose test (RPGT), or causal test, a blood sample is taken if signs of diabetes are present. The test can be done anytime. As with the last blood sample of an OGTT, a value of 200 mg/dL or more (>11.0 mmol/L) is considered high.

Continuous monitoring

Continuous glucose monitoring (CGM) is where a small monitor is kept in a vein and blood glucose levels are sampled every ≈5 minutes. The CGM monitor can be wirelessly connected to a small medical device or cell phone to notify the wearer if their blood sugar falls too low or rises too high. All diabetics can use CGMs, but they’re most commonly used by those with type 1 diabetes.

Notably, a CGM makes it possible to assess glycemic variability. This is important, because research suggests that glucose swings increase oxidative stress, which is a risk factor for diabetic complications, independent of average glucose levels.[10][11][12]

What are the symptoms of abnormal blood glucose levels?

Symptoms of abnormal glucose levels are different from person to person and may not even be present until the levels are very high or very low. Generally, blood sugar symptoms may show up when levels fall below 70 mg/dL (3.9 mmol/L) or over 180 mg/dL (10 mmol/L).

Symptoms of high and low blood glucose
LOW BLOOD GLUCOSEHIGH BLOOD GLUCOSE

Anxiety
Blurred vision
Changes in behavior or personality
Clammy skin
Confusion
Difficulty speaking
Disorientation
Dizziness or lightheadedness
Fast or irregular heartbeat
Fatigue
Feeling shaky or jittery
Headache
Hunger
Lacking coordination
Nausea
Seizure
Sleepiness
Sweating
Weakness

Blurry vision
Dry mouth
Dry skin
Fatigue
Frequent urination
Fruity breath odor
Increased thirst
Nausea and vomiting
Rapid heartbeat
Shortness of breath
Stomach pain

What affects blood glucose

Supplements

Supplements that have been shown to have a positive effect on blood sugar regulation mostly do so by either improving insulin signaling or insulin sensitivity or decreasing the rate and amount of glucose absorbed into the body. Some notable supplements include fiber, berberine, inositol, and zinc.

The table below displays an analysis of human studies and indicates how supplements may affect blood glucose.

⚠️ Caution: Supplements can affect diabetes medications

The risk of low blood sugar (i.e., a hypoglycemic event) can increase when supplements are combined with each other or with medications meant to lower blood sugar, since their effects can be greater when taken together.

Diets & foods

Across numerous observational studies, grains, vegetables, fruits, and dairy have been consistently associated with decreasing the risk of type 2 diabetes.[13]

Multiple randomized controlled trials (RCTs) have come to similar conclusions.[14]

  • Nuts, grains, legumes, and dairy provided the greatest fasting blood sugar reductions.

  • Grains, legumes, nuts, fish, fruits, and vegetables improved HOMA-IR (a measure of insulin sensitivity) the most.

  • Grains, legumes, fruits, vegetables, and nuts provided the greatest blood sugar reductions in HbA1c tests.

Listed from most to less potent, grains, nuts, legumes, fruits, and vegetables had the greatest impact on improving overall blood sugar control.

Lifestyle

The major cause of abnormally high blood glucose is excess calorie intake and the resulting increase in fat mass. Unsurprisingly, weight loss can help. One review found that weight loss from all kinds of interventions — surgery, appetite-suppressing medicines, lifestyle interventions, or a combination — alleviates diabetes.[15]

Surprisingly, many long-term studies that used diet alone to achieve weight loss reported only modest improvements in diabetes, probably because few achieved substantial long-term weight loss.[16] Moreover, exercise in itself can help reduce the risk and severity of type 2 diabetes.[17][18][19]

Exercising regularly and maintaining a healthy weight are the two major pillars of metabolic health, but insulin resistance can be complex. As a result, the basics may not always cut it, and what’s effective for one person may not be for another. Unfortunately, researchers are often unable to explore differences between individuals, leaving diabetics to fight their disease through trial and error based on what’s effective for the majority.

Medical conditions & considerations

Stress, illness, physical trauma, and dehydration can do some strange things to your blood sugar levels. Menstrual cycles and pregnancy may also throw off your blood sugar.

Injury to the pancreas, where insulin is produced, can lead to hyperglycemia, as can hormone disorders such as Cushing’s syndrome (excess cortisol in the body), pheochromocytoma (a usually benign tumor in an adrenal gland), hyperthyroidism (high thyroid levels), and acromegaly (excess growth hormone that causes abnormally large features).

Drugs

Insulin is perhaps the most well-known and widely used drug to regulate blood sugar levels. But even commonly consumed legal drugs, such as alcohol and caffeine, can have an effect.

Effects of drugs on blood sugar
DECREASE BLOOD GLUCOSEINCREASE BLOOD GLUCOSE

Alpha-glucosidase inhibitors
Biguanides
DPP-4 inhibitors
GLP-1 receptor agonists
Indomethacin
Insulin
Meglitinides
SGLT2 inhibitors
Sulfonylureas
Thiazolidinediones

Alcohol
Beta-blockers
Birth control
Caffeine
Clozapine
Olanzapine
Oral isotretinoin
Pseudoephedrine
Statins
Steroids
Thiazide diuretics

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Human Effect Matrix

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The Human Effect Matrix looks at human studies to tell you what supplements affect Blood glucose.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Supplement Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-a Minor Very High See all 29 studies
In looking at the entirety of the data on type II diabetic persons, there does appear to be a mild reduction in fasting blood glucose despite no apparent changes in insulin sensitivity or HbA1c. No significant or reliable effect in non-diabetic persons.
grade-a Minor Very High See all 25 studies
The decrease is generally small and not particularly consistent, though it does appear to be present. The reduction is particularly apparent for those with type 2 diabetes and liver diseases, as well as in studies where participants took less than 1000 mg per day, as opposed to more (more is not better).
grade-a Minor Moderate See all 10 studies
A decrease in fasting blood glucose has been noted over time with standard supplemental doses of panax ginseng in diabetics, with this dose being ineffective in altering the blood glucose of non-diabetics; high (20g) doses may acutely reduce blood glucose in healthy persons

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Things to Note

Also Known As

blood sugar

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