Coffee first entered human lives and veins over 600 years ago.

Now we consume an average of almost two kilos per person each year – sometimes with very specific preferences about blends and preparation methods. How much you drink is influenced by genes acting on your brain’s reward system and caffeine metabolism.

Coffee can raise your blood pressure in the short term, especially if you don’t usually drink it or if you already have high blood pressure.

But this doesn’t mean you need to cut out coffee if you have high blood pressure or are concerned about your heart health. Moderation is key.

So how does coffee affect your blood pressure? And if yours is high, how much is OK to drink?

What is high blood pressure?

Blood pressure is the force blood exerts on artery walls when your heart pumps. It’s measured by two numbers:

• the first and biggest number is systolic blood pressure, which is the force generated when your heart contracts and pushes blood out around your body
• the lower number, diastolic blood pressure, is the force when your heart relaxes and fills back up with blood.

Normal blood pressure is defined as systolic blood pressure of less than 120 millimeters of mercury (mm Hg) and diastolic blood pressure of less than 80 mm Hg.

Once your numbers consistently reach 140/90 or more, blood pressure is considered high. This is also called hypertension.

Knowing your blood pressure numbers is important because hypertension doesn’t have any symptoms. When it goes untreated, or isn’t well-controlled, your risk of heart attacks and strokes increases, and existing kidney and heart disease worsens.

About 31% of adults have hypertension, with half unaware they have it. Of those taking medication for hypertension, about 47% don’t have it well-controlled.

Coffee can raise your blood pressure in the short term. (bebuntoon/Canva)

How does coffee affect blood pressure?

Caffeine in coffee is a muscle stimulant that increases the heart rate in some people. This can potentially contribute to an irregular heartbeat, known as arrhythmia.

Caffeine also stimulates adrenal glands to release adrenaline. This makes your heart beat faster and your blood vessels constrict, which increases blood pressure.

Blood caffeine levels peak between 30 minutes and two hours after a cup of coffee. Caffeine’s half-life is 3–6 hours, meaning blood levels will reduce by about half during this time.

The range is due to age (kids have smaller, less mature livers so can’t metabolise it as fast), genetics (people can be fast or slow metabolisers), and whether you usually drink it (regular consumers clear it faster).

The impact of caffeine on blood pressure from coffee (and cola, energy drinks, and chocolate) varies. Research reviews report increases in systolic blood pressure of 3–15 and a diastolic blood pressure increase of 4–13 after consumption.

The effect of caffeine also depends on a person’s usual blood pressure. An increase in blood pressure may be more risky if you have hypertension and existing heart or liver disease, so it’s best to discuss your coffee consumption with your doctor.

What else is in coffee?

Coffee contains hundreds of phytochemicals: compounds that contribute flavour, aroma, or influence health and disease.

Phytochemicals that directly affect blood pressure include melanoidins, which regulate the body’s fluid volume and activity of enzymes that help control blood pressure.

Quinic acid is another phytochemical shown to lower systolic and diastolic blood pressure by improving the lining of blood vessels, allowing them to better accommodate blood pressure rises.

Can coffee cause hypertension?

In a review of 13 studies that included 315,000 people, researchers examined associations between coffee intake and the risk of hypertension.

During study follow-up periods, 64,650 people developed hypertension, with the researchers concluding coffee drinking was not associated with an increased risk of developing the condition.

Even when they examined data by gender, amount of coffee, decaffeinated versus caffeinated, smoking, or years of follow-up, coffee was still not associated with an increased risk of developing hypertension.

The only exceptions suggesting lower risk were for five studies from the United States and seven low-quality studies, meaning those results should be interpreted with caution.

A separate Japanese study followed more than 18,000 adults aged 40–79 years for 18.9 years. This included about 1,800 people who had very high blood pressure (grade 2-3 hypertension), with systolic blood pressure of 160 or above or diastolic blood pressure of 100 or above.

Here, risk of dying from cardiovascular disease, including heart attack or stroke, was double among those drinking two or more cups of coffee a day compared to non-drinkers.

Related: Caffeine in Your Blood Might Affect Body Fat And Diabetes Risk, Study Shows

There were no associations with death from cardiovascular disease for those who had either normal blood pressure or mild (grade 1) hypertension (systolic blood pressure 140–159 or diastolic blood pressure 90–99).

The bottom line

There is no need to give up coffee. Here’s what to do instead:

1. know your blood pressure, health history, and which food and drinks contain caffeine
2. consider all factors that influence your blood pressure and health – family history, diet, salt, and physical activity – so you can make informed decisions about what you consume and how much you move
3. be aware of how caffeine affects you and avoid it before having your blood pressure measured
4. avoid caffeine in the afternoon so it doesn’t affect your sleep
5. aim to moderate your coffee intake by drinking four cups or less a day or switching to decaf
6. if you have systolic blood pressure of 160 or above or diastolic blood pressure of 100 or above, consider limiting to one cup a day, and talk to your doctor.

Clare Collins, Laureate Professor in Nutrition and Dietetics, University of Newcastle

This article is republished from The Conversation under a Creative Commons license. Read the original article.