Thursday May 14 2015
Muscle strength may be affected by cardiovascular health
"Poor grip can signal chances of major illness or premature death," the Mail Online reports. An international study has provided evidence that assessing grip strength could help identify people who were at higher risk of cardiovascular incidents such as a heart attack.
The study authors wanted to see whether muscle strength, measured by grip, can predict the chances of getting a range of illnesses, and of dying, in high-, medium- and low-income countries. To find out, they tested 142,861 people across 17 countries and tracked what happened to them over the course of four years. The study found that the chances of dying during this period were higher for people with weaker grips, as were the chances of having a heart attack or stroke.
The grip test predicted death from any cause better than systolic blood pressure did, but the blood pressure test was better at predicting whether someone would have a heart attack or stroke.
Grip tests may be a quick way of assessing someone's chances of having cardiovascular disease, or dying from it, but the study doesn't tell us whether muscle weakness causes illness, or the other way around.
It is unlikely that a "grip test" would replace standard protocols for diagnosing cardiovascular diseases, which rely on a combination of risk assessment methods and tests, such as electrocardiogram (ECG) and a coronary angiography. However, such a test could be useful in areas of the world where access to medical resources is limited.
Where did the story come from?
The study was carried out by researchers from 23 different universities or hospitals, in 17 different countries. It was led by researchers at McMaster University in Ontario, Canada, and funded by grants from many different national research institutes and pharmaceutical companies. The study was published in the peer-reviewed medical journal The Lancet.
The media reported the study reasonably accurately, although the Mail and The Daily Telegraph seemed to confuse the maximum grip strength measured by dynamometer with the strength of a person's handshake, which isn't the same thing. You would hope that somebody shaking your hand wouldn’t try to grip it as powerfully as possible.
What kind of research was this?
This was a longitudinal population study carried out in 17 countries, with high, medium and low income levels. It aimed to see whether muscle strength, measured by grip, could predict someone's chances of illness or death from many different causes. As this was an observational study, it can't tell us whether grip strength is a cause of illness or death, but it can show us whether the two things are linked.
What did the research involve?
Researchers recruited 142,861 people from households across the 17 countries included in the study. They tested their grip strength and took other measurements, including their weight and height, and asked questions about their:
- activity levels
- general health
They checked up with them every year for an average of four years, to find out whether they were still alive and whether they had developed certain illnesses. After four years, the researchers used the data to calculate whether grip strength was linked to a higher or lower risk of having died or developed an illness.
The researchers aimed to get an unbiased sample of people from across the countries involved. They tried to get documentary evidence about cause of death, if people had died. However, if that was not available, they asked a standard set of questions of the people in their household to try to ascertain the cause of death. Most people in the study had their grip strength tested in both hands, although some at the start of the study had only one hand tested.
The data was analysed in a number of different ways, to check whether the results were consistent across different countries and within the same country. One big problem with this type of study is reverse causation. This means that the thing being measured – in this case, grip strength – could be either a cause or a consequence of illness. So someone with a weak grip might have weak muscles because they are already ill with a fatal disease. To try to get around this, the researchers analysed the figures excluding everyone who had died within six months of being enrolled in the study, and another analysis excluding everyone with cardiovascular disease or cancer at the start of the study. The results were adjusted to take account of age and gender, because older people and women, on average, have weaker muscle strength than younger people and men.
What were the basic results?
The researchers had follow-up data for 139,691 people, of whom 3,379 (2%) died during the study. After adjusting their figures, researchers found that people with lower grip strength were more likely to have died during the study, whether from any cause, cardiovascular disease or non-cardiovascular disease. People with low grip strength were also more likely to have had a heart attack or stroke. There was no link between grip strength and diabetes, hospital admission for pneumonia or chronic obstructive pulmonary disease (COPD), injury from falling, or breaking a bone. The results did not change significantly when excluding people who died within six months, or who had cancer or cardiovascular disease at the start.
Grip was measured in kilograms (kg) and adjusted for age and height. Average values for men ranged from 30.2kg in low income-countries to 38.1kg in high-income countries. On average, across all study participants, a 5kg reduction in grip strength was associated with a 16% increase in the chance of death (hazard ratio 1.16, 95% confidence interval 1.13 to 1.20). Grip strength alone was more strongly associated with the chance of dying from cardiovascular disease (such as a heart attack or stroke) than systolic blood pressure – a more commonly used measurement. However, blood pressure was better at predicting whether someone was going to have a heart attack or stroke.
How did the researchers interpret the results?
The researchers said their findings showed that muscle strength is a strong predictor of death from cardiovascular disease and a moderately strong predictor of having a heart attack or stroke. They say that muscle strength predicts the chances of death from any cause, including non-cardiovascular disease, but not the chances of getting non-cardiovascular illness.
They go on to say that these findings suggest muscle strength may predict what happens to people who get illnesses, rather than just predicting whether they get ill. When they looked at what happened to people who got ill, whether from cardiovascular disease or other causes, those who had low grip strength were more likely to die than those with high grip strength.
They say they cannot tell from the study why there is an association between muscle strength and chances of getting cardiovascular disease. They say further research is needed to see whether improving muscle strength would cut the chances of having heart attacks or strokes.
These are interesting results from a range of very different countries, showing that people with low muscle strength may be at higher risk of dying prematurely than other people. Earlier studies in high-income countries had already suggested that this was the case, but this is the first study to show it holds true across countries from high to low incomes.
The study also shows that Europeans, and men from high-income countries, on average, have higher grip strength than people from lower-income countries. Interestingly, women from middle-income regions, such as China and Latin America, had slightly higher muscle strength than women from high-income countries.
What we don't know from the study is why and how muscle strength is linked to the chances of death. It might seem obvious that people who are weak and frail are more at risk of death than other people, but we don't know whether this is because they are already ill, or whether their weak muscle strength makes them more vulnerable to getting ill, or less able to survive illness if they do get sick.
Importantly, the study doesn't tell us what can be done for people with low muscle strength. Should we all be doing weight training to increase our strength, or would that make no difference? Low muscle strength may reflect lots of things, such as the amount of exercise people do, what type of diet they eat, their age and occupation. We know that muscle strength declines as we age, but we don't know the effect of trying to halt this decline.
Should doctors routinely measure people's grip strength to test their health? The researchers say it is a better predictor of cardiovascular death than blood pressure, and could be easily used in lower-income countries. But raised blood pressure and cholesterol both increase the risk of cardiovascular disease, and there are treatments available to get them under control. Simply measuring a person’s grip strength would miss this opportunity and not lead to any preventive strategies.
The "grip test" could be used in poorer countries as a quick way to identify people who might be at risk of heart attack or stroke, who could then benefit from follow-up testing.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.