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What’s normal? Blood pressure, blood glucose, body temperature

Have you ever wondered how 98.6° Fahrenheit or 37° centigrade became “normal” body temperature? In the 1850’s, a German physician named Carl Wunderlich collected data on 25,000 patients, taking their temperature multiple times. Wunderlich was the first to show how the body temperature fluctuates naturally throughout the day and night, and he was the first to set the threshold for fever (any temperature above 100.4 F.)

But Wunderlich’s scientific method intrigued and challenged one very creative thinker. Philip Mackowiak, who is a medical doctor (internal medicine) and professor of medicine and medical historian at the University of Maryland, was interested in clinical thermometry, or the measurement of body temperature.  He was able of obtain one of Wunderlich’s original thermometers.

To make a fun story short (and you can listen to the entire podcast on Freakonomics here), Mackowiak describes the thermometer as unwieldy and non-registering, meaning it has to be read while it’s in place. In addition, Wunderlich only measured armpit (axillary) temperatures, and today we know that the most accurate measurements are by mouth or better, rectal temperature. Body temperature varies from one person to another. In women, it increases with ovulation and during the menstrual cycle. During vigorous exercise temperature increases.

Wondering about the historical accuracy of “normal,” Mackowiak set up his own experiment. Mackowiak learned that a person’s temperature is “almost like a fingerprint” and is unique to the individual. In his modern study he found the actual “normal” temperature to be 98.2 degrees.

My “normal” temperature is 96.8°. What’s yours?

Blood Pressure

There are many myths associated with high blood pressure (HTN), the most important one is that if you have it, you have symptoms. But that is wrong. Unfortunately, often the first symptom is stroke, or even death.

Like type 2 diabetes, once you have HTN, if you do have symptoms like headache, nosebleeds or blurry vision, it means the HTN has reached “severe and possibly life-threatening levels” according to Dr. Daniel Pohlman, a primary care doctor at Rush University Medical Center.

The only way to know if you have HTN is to get it checked regularly. And although the risk increases with age, even children can develop it, so they should be checked routinely, beginning at age three.

But measuring blood pressure needs to be done correctly.  According to Dr. William B. White, editor of the medical journal Blood Pressure Monitoring, blood pressure is measured incorrectly about 50% of the time. Nutrition Action lists common mistakes when measuring blood pressure:

  • After consuming caffeine, which temporarily raises pressure
  • Within 30 minutes of smoking — raises blood pressure
  • If your bladder is full — raises pressure
  • Within 30 minutes of aerobic exercise, such as jogging or even brisk walking — temporarily lowers pressure
  • Sitting on a exam table or chair without back support — can raise diastolic (the lower number) pressure
  • Sitting with legs dangling or crossed — raises pressure (keep your feet flat on the floor)
  • With your arm above or below heart level. The person measuring your arm should be supporting your arm, not you
  • Don’t speak — stay calm, because even casual conversation can raise pressure


One thing that can definitely raise your blood pressure is YOU! You may be like the 20% or more of patients who have “white coat syndrome”, where your blood pressure surges when measured in a clinical setting like the doctor’s office.

The Harvard Health Letter reports that blood pressure changes day to day and hour to hour, even minute to minute. They suggest that people with high blood pressure who check it consistently at home tend to be more successful in keeping it under control. Use an automatic monitor with a cuff that fits around your arm and that tracks your readings, or keep a detailed diary. Click here for a comprehensive article plus a video about the correct way to check your own blood pressure.

Two numbers represent blood pressure. The higher (systolic) number shows the pressure while the heart is beating. The lower (diastolic) numbers shows the pressure when the heart is resting between beats. According to Blood Pressure UK, ideally, we should all have a blood pressure below 120 over 80 (120/80). At this level, we have a much lower risk of heart disease or stroke.

Blood Glucose

Chronic high blood glucose is a primary risk factor for development of complications in diabetes, such as damage to nerves (leading to neuropathy), to blood vessels of the retina (diabetic retinopathy), cardiovascular disease, non-healing wounds and fungal infections, and more. Blood glucose and blood sugar mean the same thing — the sugars we eat, from fruit, lactose, starches or just simple carbohydrates are all converted into glucose, which provides fuel for our body.  We need insulin, a hormone released from the pancreas, to “unlock” the cells so the glucose can be utilized.

Prevention of type 2 diabetes, which affects 80%-plus patients with diabetes, may be possible with lifestyle modification, weight loss and consistent activity. Testing frequently is essential to good health.  After all, what you don’t know can hurt you, but when you know there’s a problem, you can take steps to solve it.

Normal blood glucose numbers
Normal for person without diabetes: 70–99 mg/dl (3.9–5.5 mmol/L)
Official American Diabetes Association recommendation for someone with diabetes: 80–130 mg/dl (4.5–7.2 mmol/L)

2 hours after meals
Normal for person without diabetes: Less than 140 mg/dl (7.8 mmol/L)
Official ADA recommendation for someone with diabetes: Less than 180 mg/dl (10.0 mmol/L)

HbA1c  Hemoglobin A1c is blood test that shows your average blood glucose over the previous 2-3 months.
Normal for person without diabetes: Less than 5.7%
Official ADA recommendation for someone with diabetes: 7.0% or less

Have your blood glucose tested on a yearly basis, especially if you have risk factors for type 2 diabetes, including a family or personal history of high blood glucose and/or diabetes, if you’re overweight or obese, and if you’re sedentary and have symptoms (blurred vision, unexplained weight loss, unusual thirst, slow wound healing, fatigue.)

Some blood glucose monitors are more accurate than others, but experts say that technique is typically the reason for inaccurate readings. There are a number of factors that can affect accuracy:

  • Damaged or outdated test strips
  • Extreme temperatures: keep meter and strips at room temperature
  • Proper coding: some meters must be coded to your particular test strips
  • Monitor use/functionality: make sure you’re inserting the strip properly, and that the batteries are up to snuff.
  • Sample size: most monitors need a generous drop of blood to get an accurate reading.
  • Red blood cell count: dehydration can skew your numbers; if you have anemia the reading is likely to be less accurate.


A good idea is to bring your monitor with you to your next doctor’s appointment or when you’re going to the lab for new tests. Check your own blood glucose level with your meter at the same time as you’re getting blood drawn for your tests.  Results within 15% of the lab reading are considered accurate.


Blood Pressure UK. What is normal blood pressure? Is there a cure for diabetes?

Diabetes Self-Management. What is a normal blood sugar level?

Freakonomics Radio. Bad Medicine, Part 1. The Story of 98.6

Harvard Health Letter. Checking blood pressure: Do try this at home.

JAMA Network. A critical appraisal of 98.6°, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich. Diabetes. Sometimes my blood glucose monitor seems to give incorrect readings. What can I do to make sure the measurement is accurate?

Nutrition Action. Don’t let your doctor make these 9 blood pressure measurement mistakes.

Rush University Medical Center. Myths about high blood pressure.

University of Michigan Health System. Body Temperature.


9 thoughts on “What’s normal? Blood pressure, blood glucose, body temperature

  1. Fascinating. My highest temp. ever recorded was 97.0. Seems 96.3 is my most common…no matter where or when. This is such important info, Susan. Hope everyone reads it! Thank you.

  2. Great article, Susan! I keep a blood pressure cuff handy by my bedside and monitor it a couple times a week. I no longer take blood pressure medication and my most recent reading was 111/68 with a pulse reading of 61. Now I need to get in for a series of blood tests to check my cholesterol and other things!

  3. The AccuChk telephone RN told me that the blood glucose can vary as much as 20 points from one hand to the other with that equipment. Because an individual’s reading is often a certain level doesn’t mean it is “normal” for them, but simply usual. Would be interesting to know if anyone has ever checked the difference between vegan and non-vegan average blood glucose levels. Do you know?

  4. Mason, the RN is correct, and just like blood pressure fluctuates, stress, illness, diet and activity can affect blood glucose readings. Your diet as part of your healthy lifestyle affects your weight and thus your blood pressure and blood glucose, however, you can be healthy and include moderate amounts of animal protein in your diet and you can be healthy by excluding animal products too. The major world health organizations all recommend a plant-based diet for best health outcomes, and conversely, people who eat the greatest amounts of “free sugars” (added sugars, junk food) and processed meats are far more likely to be sick.

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