Blood pressure in the cold: why readings rise in winter

In February the device reads 138 over 88. In July, with the same device, on the same arm, at the same time of day: 128 over 80. Many people know this jump from their own record sheet and take it for a fault – in the device or in themselves.

It is neither. Blood pressure follows the outside temperature, and it does so in a predictable direction. The interesting question is how much of it happens in the body – and how much only in the measurement.

Why blood pressure rises in the cold

Cold triggers a response that protects the body against heat loss: the vessels in the skin and in other regions of the body narrow. Less blood flows to the places where it would cool down.

The price for that is pressure. The narrower the vessels, the greater the resistance the heart has to pump against. The German Heart Foundation puts it this way: the heart has to move the blood through the arteries „against a greater resistance“. That places a load on the heart muscle and on the vessel walls.

A second effect is mentioned less often: in the cold, the blood's tendency to clot and its viscosity both increase. So it is not only narrower – the blood itself flows more thickly.

How clearly this can be measured is shown by a Japanese study in healthy subjects: at a room temperature of 24 °C, blood pressure readings were measurably lower than at 14 °C. Ten degrees of room temperature are therefore enough to make a difference visible – with no winter walk required.

How large the effect is – and in which unit

This is where it gets uncomfortably precise, and for a good reason: figures circulate on this topic that cannot be substantiated.

What can be substantiated comes from an analysis the German Hypertension League points to. It did not compare „winter against summer“, but examined something finer: skin temperature as the intermediate link between outside temperature and blood pressure.

The values therefore do not refer to seasons, but to one standard deviation of skin temperature. If skin temperature rises by that amount, the systolic value changes as follows:

• during the day, at the hands and feet: −4.27 mmHg
• during the day, at the trunk: −2.74 mmHg
• at night, at the hands and feet: −2.62 mmHg
• at night, at the trunk: −2.68 mmHg

These figures are not an answer to the question „how much higher is my blood pressure in winter?“ They measure something else, in a different unit. Converting them into „X mmHg more in January“ means inventing a number.

The honest answer is this: the direction is unambiguous, the effect is measurable, and its size depends on you and on your surroundings. Which is exactly why your own series of readings says more than any average from a study.

The hands reveal more than the belly

The most interesting line in the list above is the first one. Look at the difference between the extremities and the trunk during the day: −4.27 against −2.74 mmHg.

The analysis puts it even more plainly: per degree of outside temperature, the effect mediated through the skin is around seven times as strong at the extremities during the day as at the belly. At night this difference largely disappears.

For measurement this has a consequence that is written down almost nowhere: if your hands are cold, the value the cuff displays is already shifted by that alone. Not because your circulation is running out of control, but because the measuring condition has changed.

It is the same mechanism that otherwise makes your blood pressure different at every measurement – except that in winter it does not fluctuate at random, but pulls systematically in one direction.

The authors of the analysis are cautious at this point, and that belongs in the picture: whether deliberately keeping hands and feet warm can prevent cold-related rises in blood pressure still has to be clarified by intervention studies. The association has been observed – the benefit of any measure is not thereby proven.

What this means for your measuring routine

Four practical points follow from the findings above. They cost nothing and they make your winter readings comparable:

• Do not measure straight after coming home. Anyone who has just come in from the cold is measuring a snapshot of vessel narrowing, not their resting blood pressure.
• Warm your hands first. Five minutes of rest are mandatory anyway – in winter, sensibly five minutes in a warm room.
• Note the room temperature. A record sheet with a „room cold / warm“ column explains more in hindsight than any recollection.
• Always measure in the same room. Kitchen in summer, bathroom in winter – that is not a comparison.

Everything else about measuring cleanly – cuff fit, arm height, the interval between two readings – is covered in Measuring blood pressure correctly. Which time of day makes sense is explained in When should you measure blood pressure?.

And if you want to know how the same mechanics work in the other direction in summer: Blood pressure in the heat describes the counterpart – wide vessels, fluid loss, falling readings. The two articles belong together.

Who should pay particular attention in winter

The German Heart Foundation names several groups in whom cold places a greater load on the circulation:

• coronary heart disease (CHD) and the state after a heart attack
• angina pectoris
• high blood pressure and heart failure
• atrial fibrillation
• deep vein thrombosis

In addition there are possible links with strokes, pulmonary embolisms and certain rhythm disturbances. If you belong to one of these groups, the cold season is a good occasion to document your own readings more closely again – and to know what your numbers mean.

Shovelling snow and other exertions

The combination that professional societies warn about most clearly is cold plus sudden strong exertion. Shovelling snow is the standard example: cold air, narrowed vessels, and on top of that a vigorous effort from a standing start.

The German Heart Foundation's recommendation is correspondingly concrete: avoid such peak exertions and go for a walk instead. A scarf over mouth and nose pre-warms the air you breathe. In severe frost, training can be moved indoors.

That leaves the question many people have in winter: does the medication need adjusting? The Heart Foundation states that a dose adjustment can be one solution where readings rise because of the cold – and that this decision belongs in medical practice.

Never change the dose, the timing or the way you take your medication on your own. What you can do: take a documented week to your next appointment and raise the subject of the season yourself. That makes the conversation considerably more productive than the recollection that it was „higher in winter“.

When to seek medical advice

• If your readings stay clearly above your usual level for several weeks – including when you believe the cold is the cause
• With pressure or tightness in the chest, or shortness of breath, during or after exposure to cold
• If you belong to one of the groups above and are unsure how to measure through the winter
• Before any thought of changing anything about your medication

In case of sudden severe chest pain, shortness of breath, cold sweat, speech or vision disturbances or one-sided paralysis: call the emergency services on 112 immediately.