Giving blood is an excellent way to help others and, if you have high blood pressure, it may help you too.
A German study involving 292 blood donors, who gave blood on up to four occasions within a year, found their average blood pressure reduced with each donation.
Giving blood lowers blood pressure
Half of those taking part had a normal blood pressure (below 140/90 mmHg) and half had a high blood pressure that was greater than 140/90 mmHg.
Of the group that had hypertension, 146 donated at least once, 114 donated blood at least twice, 66 on at least three times, and 39 gave blood on four occasions over the year.
At each visit to give blood, their blood pressures were rechecked four times before each donation, to obtain an average reading, and three times after each donation.
Immediately after each donation, systolic blood pressure (the upper reading) fell by an average of 3.3mmHg in those with normal blood pressure, and by 7.1mmHg in those with hypertension, while diastolic blood pressures (lower figure) remained fairly constant.
This immediate effect of giving blood is to be expected due to loss of blood volume, as each donation removes around 480 ml blood from your circulation. This volume is soon replaced by the extra fluid you are encouraged to drink, however, and the circulation naturally adjusts.
The really interesting finding, however, was that each donation also reduced average blood pressure going forwards.
Giving blood may have lasting blood pressure benefits
On each subsequent visit to give blood, average blood pressure readings in those with hypertension were lower than on the previous visit.
In those with high blood pressure who gave blood on four occasions, average blood pressure decreased by 12.2/6.9 mmHg (from 155.9/91.4 mmHg down to 143.7/84.5 mmHg).
Those classified as having stage II hypertension (blood pressure greater than 160/100 mmHg) had the most marked reduction with an average fall in blood pressure of 17.1/11.7 mmHg after four blood donations.
As a result of giving blood regularly, some of those with high blood pressure (7.5%) had their antihypertensive medication reduced by their doctors, and some (5%) had their drug therapy stopped altogether. Only 6 people (4%) had to have their blood pressure medication increased.
Some people (9%) did develop low haemoglobin levels however, and were prescribed iron supplements, but most chose to continue donating blood once their iron levels came back up to normal.
The researchers concluded that this beneficial effect of blood donation may offer an effective way to help manage high blood pressure.
How giving blood lowers blood pressure
The obvious way in which giving blood might lower a high blood pressure is by reducing the volume and stickiness of blood in your circulation as blood is diluted by retained fluid. Giving blood may also reduce the level of ‘bad’ non-HDL cholesterol and reduce the oxidation of blood lipids (eg LDL-cholesterol, triglycerides) by reducing levels of iron or the iron binding protein, ferritin.
However, other researchers have suggested that while donating blood on a regular basis appears to reduce blood pressure, appearances can be deceiving. These researchers analysed blood pressures taken during 91,518 first blood donations, and checked them against the results when the same donors attended again on up to four occasions. On average, donors whose blood pressure was raised during one of these visits had relatively normal values during other donations, whether or not these were before or after the high reading.
It’s also possible that in the initial study, blood pressures were artificially high on the first visit due to the effects of white coat hypertension and the stress of anticipating the needle. As people became more comfortable with the experience of giving blood, this could explain why their blood pressures came down on each subsequent occasion.
The only way to find out if giving blood improves your blood pressure readings is to try it and see, while helping others at the same time.
Can you give blood if you have high blood pressure?
According to blood.co.uk, if you have high blood pressure you can usually give blood if:
- you are being managed on diet and lifestyle without medication or if you have been on the same dose of the same medication for 4 weeks or more and feel fit and well
- you have not suffered from heart failure in the past
- you don’t have kidney problems
- you have not had an amputation or blood vessel surgery
- you have never had gangrene
- you have no problems with fainting, feeling faint or giddiness.
When you make the appointment to give blood, let the staff know about any medications you are taking.
If you are taking antihypertensive medication, this can be noted on your donation so that it is not given to someone who is in clinical shock (very low blood pressure) or who is allergic to that medicine.
Should you stop your blood pressure medicine on the day of donation?
You will need to ask your own doctor whether or not you should take your antihypertensive medications on the day of your donation.
I usually advise people to book an early appointment, and to miss their early morning blood pressure medication. This helps to ensure their donation contains very little of the drug they are taking, and also helps to reduce the chance of developing hypotension (low blood pressure) and feeling faint or dizzy after donating.
It’s then a good idea to monitor your blood pressure throughout the rest of the day and to take your medication if your blood pressure rises above your target readings.
Your own doctor may disagree, based on your past medical history and how well your blood pressure is generally controlled, so please ask their advice first.
And always mention any medication you are taking to the staff at session before you donate.
If your blood pressure is raised, self-monitoring is important to maintain good control.
Click here for advice on choosing a blood pressure monitor to use at home.