Monthly Archives: February 2017

What is Normal Blood Pressure? 120/80 vs 115/75

If you don’t know your blood pressure, it’s like not knowing the value of your company. –Mehmet Oz1

I’ve been re-reading much of Ray Kurzweil’s fascinating TRANSCEND recently with a focus on his explanations on blood pressure. The book claims that “optimal” blood pressure is anything under 120/80. You’ve probably heard 120/80 referenced as “normal” blood pressure by your doctor, and you might think you only need to worry about reducing blood pressure if it’s over 120/80 or even 140/90. But the truth, as backed up by the reports that introduced 120/80 as the “normal” standard 15 years ago, is that the risk of cardiovascular disease starts increasing at 115/75, and the healthy range is between 90/60 and 115/75.

Where does 120/80 come from?

In the early 1900s, insurance companies in the USA wanted better ways to predict when and why people would die. In 1906, suspecting the clinical significance of high blood pressure, they started measuring the blood pressure of applicants for life insurance. In the coming years this idea spread, and by 1925 there was a study published by the Actuarial Society of America that involved over 10 million participants and measured the relationship between blood pressure and mortality. One of its key findings was that

mortality increases rapidly with the increase in blood pressure over the average2

Many studies have been run since then. Some focus on mortality, while others focus on heart disease and other outcomes. A notable study from 19933measured stroke, cardiovascular diseases, life expectancy, and mortality from all causes, including coronary heart disease. The authors claim they found a strong relationship between blood pressure, and these outcomes, suggesting 120/80 as the upper bound on “optimal” blood pressure.

Then in 2003, new guidelines45were published in JAMA that classified normal blood pressure as anything under 120/80 instead of the previous 129/84.These guidelines have been adopted by many reputable sources that now claim anything under 120/80 to be normal.678

However, the report also stated that

The risk of cardiovascular disease begins at 115/75 mm Hg and doubles with each increment of 20/10 mm Hg9

This is why the upper bound on blood pressure readings that you should consider healthy for yourself is 115/75 instead of 120/80.

These reports do not focus on a single number that they claim to be perfect for everyone. Instead there are ranges of numbers that are classified as normal or otherwise.

What’s Wrong with 120/80?

There’s nothing wrong with using 120/80 as a bound on ranges with classifications. It makes perfect sense if that’s what the data suggests to be meaningful. The problem lies with giving the number more meaning than it really has, or believing that you have nothing to worry about just because your blood pressure is under 120/80. This problem is exacerbated by the common belief, reinforced by reputable sources, that anything under 120/80 is great.

For example, a 2003 article from Harvard Medical School10stated that if your blood pressure is less than 120/80 then you should “Keep up the good work!”

Is it really as simple as that? How do they know what “work” you’ve been doing?

What if over the last 5 years your blood pressure has slowly risen from 110/70 to 119/79? That’s an increase of about 9%, and at that rate your blood pressure would be 129/86 in another 5 years, which is too high. Results like this should concern you, and you shouldn’t “keep up the good work”. This is a simplistic example, but it stands to reason that if you are experiencing a significant upward trend in your blood pressure, and you don’t know why it is happening or have any reason to believe that it will plateau, then you should probably take action (with help from your doctor, of course).

This means that it can be helpful to keep track of your blood pressure over time, and consider taking action if you notice significant or sudden upward trends, even if you’re still under that 120/80 bound.

Why is 90/60 the lower bound?

Blood pressure readings of 90/60 or lower are a sign of low blood pressure11which carries its own health risks such as confusion, weakness, and fatigue.

What other factors affect normal blood pressure?

Even with data to show that a healthy range is 90/60 to 115/75 there can be exceptions. Your age can be an important factor in what is considered normal blood pressure. For children, the Blood Pressure Tables for Children and Adolescents12show that normal blood pressure readings for boys range from 85/37 to 118/67 from ages 1 through 17. For the elderly, normal blood pressure readings can be higher, and there is data to suggest13 that 140/80 is a healthy reading for people aged 70 and older.

Conclusion
  • For most people, normal blood pressure should be under 120/80
  • Factors like age can affect your expected normal blood pressure
  • Health risks start increasing for blood pressure over 115/75
  • Don’t wait until you get a high reading to take action. If your blood pressure rises significantly over time then it can help to address it before it gets too high.

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