Thursday May 1 2014
Cocaine use was found to damage the heart
"Even 'social' cocaine users are doing catastrophic damage to their hearts," the Mail Online reports after an Australian study found that casual cocaine use was associated with heart damage.
Most previous research into the effects of the illegal stimulant has involved people recruited through drug treatment centres. As the researchers point out, these people may not be representative of the majority of cocaine users – "dinner party drug users", who may regularly use the drug once or twice a week.
The researchers recruited 20 people who described themselves as regular cocaine users, and used imaging techniques to compare their heart and vascular function with 20 controls (people who didn't use cocaine).
They found that cocaine users had poorer heart and vascular function measures, including increased aortic stiffness and systolic blood pressure, and greater left ventricular mass. These are well-known risk factors for early cardiovascular events such as a heart attack.
The study was small and cannot prove a direct cause and effect relationship between cocaine use and heart damage. But it does add to the growing body of evidence that even semi-regular drug use can be dangerous.
Where did the story come from?
The study was carried out by researchers from the universities of Sydney and New South Wales and Royal North Shore Hospital. It was funded by a grant from Heart Research Australia.
The study was published in the peer-reviewed open access journal PLOS ONE, so it is free to read online.
The Mail Online's reporting of the study was reasonably accurate and included some useful background quotes, although it failed to report the limitations of the study.
What kind of research was this?
This was a case-control study that looked at whether or not cardiovascular abnormalities were present in healthy people who consider themselves social cocaine users (cases), compared with non-users (controls).
It was cross-sectional in nature as all participants were tested at one point in time. However, because this study only looked at one point in time, it cannot establish cause and effect between factors, as it does not show which of them came first.
Cocaine addiction has previously been associated with heart disease, but the researchers wanted to study its effects in people not considered to be addicted.
According to a 2010 national Australian survey, 7.8% of Australians aged 18 and over had used cocaine in their lifetime, with 2.1% having used it in the previous 12 months.
A similar pattern can be found in the UK, with 1.9% of adults reporting to have used cocaine in the previous 12 months according to a 2013 Home Office survey.
What did the research involve?
The researchers recruited 20 people aged 18 or older who described themselves as regular cocaine users and 20 people who were non-users. All participants were employed and were recruited by word of mouth in an affluent area of Sydney.
Cocaine users were not recruited from drug rehabilitation centres to attempt to minimise the inclusion of cocaine addiction or dependence and reflect the majority of cocaine use in Australia (young and employed people who use cocaine on a recreational basis).
Regular cocaine use was defined as at least monthly use in the 12 months prior to the start of the study and non-use was considered as no prior cocaine use. People were excluded from the study if they had known heart disease or previous heart attack.
All participants underwent cardiovascular magnetic resonance imaging (CMR), a type of non-invasive imaging process used to accurately measure the heart and vascular function, including systolic blood pressure and aortic stiffness.
None of the participants reported using cocaine in the 48 hours prior to CMR testing, which was an exclusion criterion.
Participants also completed a researcher-designed questionnaire that detailed demographic details, history of substance abuse, and cardiac (heart) risk factors.
The researchers then compared the results of the CMR testing for cocaine users and non-users.
They also took some potential confounders into account as part of their analysis, such as:
- body surface area (obtained from weight and height)
- smoking history
- alcohol use
What were the basic results?
Most of the participants were male (90%). Among cocaine users, most people inhaled the drug nasally (16/20 people [80%]), with three people who smoked it (15%) and one person who injected it (5%).
The main findings presented in the research are for the 40 participants recruited by word of mouth. There were significant differences in the characteristics between cocaine users and non-users in this group of 40. The cocaine users were significantly more likely to be smokers, drink more alcohol and use other illicit drugs in their lifetime compared with non-users.
The researchers therefore excluded four individuals from the non-use group who were non-smokers and had no alcohol history, and replaced them with four non-users who were smokers with moderate alcohol consumption.
Despite this re-matching, it remained that cocaine users were significantly more likely to use other illicit drugs more than non-users. A small analysis using the re-matched controls was presented in the supplementary material of this study. Results are provided below for both the original group of 40 and the re-matched group where this was carried out.
The main findings of the study were:
- a significantly higher systolic blood pressure was seen among cocaine users (134 mmHg) compared with non-users (126 mmHg) – this finding remained significant in the re-matched analysis
- cocaine use was associated with increased arterial stiffness (a negative finding that was independent of vessel wall thickness)
The increased arterial stiffness was reflected by:
- a reduced aortic compliance among cocaine users (1.3 mmHg-1) compared with non-users (1.7 mmHg-1) – this finding remained significant in the re-matched analysis
- decreased distensability among cocaine users (3.8 mmHg-1) compared with non-users (5.1 mmHg-1)
- increased stiffness index among cocaine users (2.6) compared with non-users (2.1)
- higher pulse wave velocity among cocaine users (5.1 m.s-1) compared with non-users (4.4 m.s-1)
In addition, the researchers also found:
- a significantly higher left ventricular mass was seen among cocaine users (124) compared with non-users (105), representing an 18% increase among cocaine users – this was independent of age, gender, smoking and alcohol use, and the finding remained significant in the re-matched analysis
- increased left ventricular mass, systolic blood pressure and vascular stiffness were all associated with duration and frequency of cocaine use
How did the researchers interpret the results?
The researchers concluded that compared with the non-user controls, cocaine users had increased aortic stiffness and systolic blood pressure associated with a greater left ventricular mass. These measures are all well-known risk factors for premature cardiovascular events, highlighting the dangers of cocaine use, even in a "social" setting, and have important public health implications.
Lead researcher Professor Gemma Figtree, from the University of Sydney, is quoted in the media as saying: "While some people who use cocaine recreationally may not think that they are doing their body a lot of harm, our results show this is not the case and that cocaine is dangerous for your health even when taken socially."
Overall, this study provides some evidence of negative differences between social cocaine users and non-users in heart and vascular function detected by image testing.
There are several limitations of this study that are worth noting, however, including the fact that it was only carried out at one point in time, so it cannot show that cocaine use was responsible for the differences seen.
The size of the study
This was a relatively small study, with only 40 participants, who were predominantly male. The findings therefore may not be generalisable to large numbers of people or to female cocaine users. Despite this size limitation, the researchers report the study was adequately powered to detect differences between the groups in the main outcomes.
Poorly matched groups
Compared with non-users, cocaine users were more likely to be smokers and have a higher self-reported usage of other illicit drugs in their lifetime, which may have been a contributing factor. This led to the researchers replacing four of the non-users with non-users that were better matched to the cocaine users (they were smokers and had moderate alcohol consumption). Instead of presenting results for this overall better-matched group, only three findings were reanalysed, with the majority of results presented for the poorly matched groups.
Reliability of information provided
Participants had only one study visit and all information provided was by self-report. This included information about cocaine use or non-use, smoking status, alcohol consumption and illicit drug use. It is recognised that gathering this information reliably from social cocaine users would be difficult, but the possibility remains that participants did not accurately report this information, which may have biased the results.
With these limitations in mind, cocaine use, especially when combined with alcohol, has been implicated in many premature deaths in young adults. Combining the two drugs creates a third drug called cocaethylene, which can cause damage to both the heart and liver.
For more information, visit the Drinking with Charlie website.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.