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What Factors Affect Blood Pressure Readings?

Blood pressure readings can be affected by a variety of factors which should be taken into consideration before jumping to any conclusions about your health from a single blood pressure measurement. These can range from very short term temporary influences, typically involving reactions to your environment or the consumption of certain foods and beverages explored below, to medium and longer term factors affecting your blood pressure readings that may require blood pressure medicine or changes to your lifestyle to correct.

In the following we will take a look at short term factors that may affect your blood pressure readings.

Short Term Influences on Blood Pressure Readings

Smoking or Vaping

Smoking a single cigarette with 1mg of nicotine has been shown to increase systolic blood pressure by +7% and diastolic blood pressure by +10% and pulse rate by 25%, particularly if it is the first cigarette of the day. Similarly vaping electronic cigarettes has also been shown to cause significant increases in blood pressure for around half an hour. If you smoke or vape, consider taking your blood pressure readings at different times of day in order to understand how your habit is affecting your blood pressure readings in the short term.

Caffeine

The consumption of caffeine can increase blood pressure dramatically in the short term, although the sensitivity of the reaction varies depending on the person. If you find that your blood pressure readings are being affected in the short term relative to your caffeine use, then try to reduce your consumption to no more than 2 cups of coffee a day equivalent (about 200 milligrams per day) and avoid using it before doing other activities that are also likely to raise your blood pressure in the short term, such as weightlifting or exercise. The US Food and Drug Administration (FDA) recommends adults not having more than 400mg of caffeine a day in general and no more than 200mg in a single serving when using tablets or concentrated powders.

Salty Food

salt and high blood pressure

Salt is known to affect blood pressure but is dependent on an individual’s sensitivity to it


The effect of salt on blood pressure varies greatly with the sensitivity of the particular person concerned and it can be challenging to identify salt sensitive individuals. For this reason many health authorities advise everyone in the population to lower their salt intake. Seeing as most diets far exceed the physiological salt requirements of around 20mmol/d and that around half of the population in the US over the age of 60 have developed hypertension, a reduction of salt in the diet for everyone is deemed a sensible recommendation. There is a possibility your own blood pressure may be affected in the short term after consuming salty food so bear that in mind.

Alcohol

In the short term, research suggests that low to high doses of alcohol may reduce blood pressure readings but 6 or so hours after consuming high doses of alcohol, blood pressure readings potentially increase. If you are taking blood pressure readings after alcohol consumption be aware they may be affected in the following hours, potentially causing either a decrease or increase in those readings.

Stress

When you are faced with a stressful situation your body releases cortisol and adrenaline, this is your “fight or flight” response to the threatening situation. It makes your blood vessels narrow and increases your heart rate and so your blood pressure rises. This acute response to stress is usually short lived but it can affect your blood pressure readings. Some people suffer from white coat syndrome which is the fear of doctors and medical facilities like hospitals. People that suffer from these sorts of conditions will likely have their blood pressure readings be higher when taken in these environments, than if the blood pressure readings are taken at home when the person is more relaxed. However, if a fear or phobia causes the person to faint “vasovagal syncope”, for example from the sight of blood, then this is due to a sudden drop in blood pressure and readings would be affected to have a lower outcome in those scenarios.

Temperature

Blood pressure readings can be affected by temperature changes to the body, with a general relationship that warmer temperatures reduce blood pressure while colder temperatures increase blood pressure, particularly if considered on a hourly basis. In the same blood pressure v temperature study alcohol drinkers were found to be more sensitive to blood pressure changes relating to the cold and their blood pressure rising, while diabetics were found to be more sensitive to heat rises and their blood pressure dropping. Another study highlighted a relationship of 1 degree centigrade decrease in ambient air temperature leading to a 1mmHg increase in systolic blood pressure. When it’s cold blood vessels tend to constrict near the skin to preserve heat, which causes a rise in blood pressure. When hot, vessels dilate to aid with cooling the blood at the skin surface, hence people look red when they are hot. If you have a long hot bath then stand up too quickly, you may feel faint. This is because the body needs time to adjust its blood pressure back to a higher level, than from when it was pumping through dilated vessels in a low pressure horizontal body position in the bath, to needing to pump blood up to the head against gravity when suddenly standing.

Exercise

When doing vigorous exercise, it is normal for your systolic blood pressure to increase significantly. This is due to the heart needing to pump oxygen via the blood into the muscles at much greater rate than when relaxed. The diastolic pressure between beats will be much less affected. If your systolic blood pressure reading when exercising gets over 200mmHg however, this is known as exercise hypertension and may indicate a problem which you should seek medical advice about. If you have serious hypertension, extreme workouts may put a lot of strain on the heart and once again speaking with you doctor about the level of exercise you wish to undertake is advisable. They may wish to lower your blood pressure with medication prior to you embarking on a new exercise regime. Overall regular exercise will reduce your blood pressure in the long run but be aware that it can impact blood pressure readings in the short term.

Phobias

Phobias are irrational fears of things or situations, about 12.5% of the population is thought to harbour such specific fears throughout their lifetime. Medical phobias such as the fear of blood or needles are typically accompanied by blood pressure rising at first and then dropping low, often low enough to induce fainting. There is even a fear of blood pressure measurement itself, referred to as BPP. If you have white coat syndrome mentioned in the above stress section or a specific phobia such as BPP, be aware that this will have an impact on your blood pressure readings over the short term.

Time of Day

Blood pressure readings will vary depending on the time of day relative to your sleep pattern. Usually blood pressure rises before you wake up and peaks around midday then drops off throughout the afternoon and evening, being at its lowest when you sleep. If your nocturnal blood pressure is not 10% below your daytime readings this is referred to as non-dipping blood pressure. There is evidence that organ damage may be a greater risk for people with non-dipping blood pressure who have essential (ie not caused by other medical afflictions) hypertension.

Summary

As seen above there are a whole host of factors that may influence the outcome of your blood pressure readings in the short term. It is important to find a reasonable average reading over several days, ideally with a home blood pressure monitor while attempting to eliminate as many of the variables mentioned above as possible. This way you will have a much better understanding of your general blood pressure status and what steps might need to be taken to improve it.

You can check out any blood pressure reading and what it means on the xBloodPressure homepage.

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