Monday May 20 2013
"Bad" LDL cholesterol can raise your risk of heart disease
'A stressful job really can kill you – by raising your cholesterol,' reports the Mail Online website. This headline is based on Spanish research that looked at the relationship between job stress and lipid (fat) levels in the blood of more than 90,000 people.
The research found that people who reported difficulties coping with their job had higher levels of what has been dubbed "bad cholesterol" (LDL cholesterol) and lower levels of "good cholesterol" (HDL cholesterol). High levels of LDL cholesterol can clog up the arteries, increasing an individual's risk of developing cardiovascular diseases such as coronary heart disease.
A significant strength of this study is its size – an impressive 90,000 people participated. But the study did not look at diet, which can also affect cholesterol levels. It could well be the case that people in stressful jobs tend to have unhealthy diets and it is this, rather than stress itself, that is to blame for their higher "bad" cholesterol rates.
While increased LDL levels are a risk factor for cardiovascular diseases, this study did not explore the effect this would have on people's long-term health. The Mail Online's claim that a stressful job will kill you is therefore not supported by this study.
Where did the story come from?
The study was carried out by researchers from Ibermutuamur – a mutual insurance company dealing with work-related accidents and occupational illnesses – and two universities in Spain. There were no external sources of funding for the study.
It was published in the peer-reviewed Scandinavian Journal of Public Health.
The Mail Online's headline over-interprets the research, as the study did not assess whether people in stressful jobs were more likely to die. The body of the story was reasonably accurate, but it did not highlight that this type of study cannot prove that one factor is definitely causing another.
What kind of research was this?
This was a cross-sectional study that explored whether there is a link between job stress and abnormal levels of fats (lipids) in the blood.
Some studies have found a link between job stress and an increased risk of coronary disease. There are various theories about how this link might come about – for example, by stress increasing the likelihood of unhealthy habits such as smoking.
Some studies have also suggested that stress could directly influence levels of lipids in the blood by possibly adversely affecting the body's metabolism. However, these studies have been small and in selected populations, and have had mixed results.
In the current study, researchers wanted to assess stress and lipid levels in a large representative sample of workers. As this study is cross-sectional, both stress and lipid levels were assessed at the same time. This means the study cannot establish whether participants' lipid levels were directly influenced by their stress levels.
What did the research involve?
The study involved workers covered by the Ibermutuamur insurance company who had yearly medical check-ups. More than 430,000 participants were recruited between 2005 and 2007, and a study questionnaire was sent out to more than 100,000 randomly selected individuals. Completed questionnaires were returned by 91,593 of these people.
The questionnaire included the question, "During the last year, have you frequently felt that you cannot cope with your usual job?". Participants who answered "yes" were considered to have job stress.
The questionnaire also included 11 questions relating to anxiety and depression symptoms, such as "Have you felt keyed up, on edge?" and "Have you had difficulty relaxing?".
The researchers took fasting blood samples from participants and measured levels of total cholesterol, HDL cholesterol (so-called "good" cholesterol), and levels of a type of lipid called triglycerides. The levels of so-called "bad" cholesterol were calculated based on these measurements.
Participants were classed as having abnormal lipid levels based on pre-specified levels if they reported taking lipid-lowering medication or had been diagnosed as having abnormal lipid levels.
The researchers then looked at whether abnormal lipid levels are linked to job stress. They took into account the following confounders:
- basic measures of alcohol consumption and physical leisure activity
- type of job ("blue collar" or "white collar")
What were the basic results?
Job stress was reported by 8.7% of participants. Participants reporting job stress also had higher levels of anxiety and depression symptoms.
After the researchers took into account factors that could affect the results and adjusted them accordingly, people who reported job stress were found to have 10% higher odds of having abnormal lipid levels (odds ratio [OR] 1.1, 95% confidence interval [CI] 1.04 to 1.17).
They also had increased odds of:
- high levels of "bad" cholesterol (LDL)
- low levels of "good" cholesterol (HDL)
- a high total cholesterol to "good" cholesterol ratio
- a high "bad" cholesterol to "good" cholesterol ratio
How did the researchers interpret the results?
The researchers concluded that their results support an association between job stress and abnormal lipid levels in the blood.
This study has found an association between job stress and abnormal lipid levels in the blood. Its strengths include the large number of workers assessed (more than 40,000) and the use of the same methods to assess all of the participants.
However, the fact that both job stress and lipid levels were assessed at the same time means it is not possible to say for certain whether job stress might have directly caused changes in blood lipid levels.
There are also other limitations and points to note:
- The study did not assess diet. People with job stress may have less healthy diets, which could account for the differences seen in the blood lipid levels, rather than these differences being a direct impact of job stress.
- Job stress was assessed by a single question, which may not fully capture all aspects of job stress. Also, different people may consider different things stressful, and the question did not disentangle the exact stressful workplace situations and an individual's ability to cope with them.
- Workers who were off sick would not have had the routine medical check-up. This means the sample may have missed some people with more serious health problems with stress.
- The authors acknowledge that the effect of job stress seen is relatively small – a 10% increase in the odds of having abnormal lipid levels.
Overall, it is not clear from this study whether stress is a direct cause of the increased lipid levels seen. Studies looking at whether interventions to reduce work stress can reduce lipid levels in the blood would provide an indication if this is in fact the case.
Despite these limitations, there is a wide range of good quality evidence that workplace stress can have a harmful effect on your physical and mental health.
While some people may thrive on pressure, persistent high levels of stress are likely to be harmful.
Read more about what you can do to reduce your levels of workplace stress.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.