Date Published: 21 March 2012

Monkey research and human health

We don't usually include as "medical news" reports of experiments on animals. However, the recent review of research involving monkeys (review undertaken and reported by experts at Bristol University) is especially noteworthy.

Background Information:
Psychosocial factors such as stress, social instability and work dynamics are often believed to play an important role in the emergence of disease, with the negative effects associated with high stress levels deriving from disturbances and sudden change. In evaluating these effects on humans, the scientific community often relies on primate models because it is easier to induce changes in their environment(s), and because of monkeys' biological closeness to us - see a comparison between humans and primates. Studies involving research using monkeys and other primates have historically provided one foundation for the suggestion that factors such as stress or position in a social hierarchy may lead to some people suffering more ill health than others.

The recent study (see Ref. below) included a systematic review to identify all studies of psychosocial factors and coronary artery disease in non-human primates via searches of several databases (MEDLINE, PsycInfo, EMBASE, and Primatelit). These searches were conducted to find experimental and observational studies of the impact of social reorganisation, social instability, and disruption of dominance hierarchies on primate coronary artery disease outcomes. The researchers also "handsearched" bibliographies and examined the citations to those studies in public health articles.

The study concluded that although studies involving experimentation on monkeys are cited frequently in human health research the evidence is often "cherry picked" and generalisation of the findings from monkeys to human societies does not appear to be warranted.

The researchers from the London School of Hygiene & Tropical Medicine and Bristol University concluded that:

" Overall, non-human primate studies present only limited evidence for an association between social status and CAD. Despite this, there is selective citation of individual monkey studies in reviews and commentaries relating to human disease aetiology. Such generalisation of data from monkey studies to human societies does not appear warranted. "

Lead author, Mark Petticrew, Professor of Public Health Evaluation at the London School of Hygiene & Tropical Medicine, said that without assessing the validity of primate studies first, there is little point in using them to build theories of causes of human ill-health.

He explained:

" Before we can apply results from primates into our society, we need to make sure that the evidence coming from these studies is reliable. Systematic reviews of animal studies are still uncommon but they are essential for assessing the consistency and strength of their findings. It is unscientific to selectively refer a same small handful of positive findings and discard all the others that do not fit the hypothesis."

The researchers also warn against generalising results from primate data to human societies and point out that many primatologists themselves have drawn attention to the limitations in reaching such conclusions, as their findings are not necessarily comparable between similar species of monkey, and sometimes not even within the same species. Too many factors are at play that can introduce bias, such as the environment the primates were brought up in, the laboratory settings and other potentially traumatic experiences like relocating from the wild to a laboratory.

The study suggests that if studies correlating social hierarchy and heart disease in monkeys cannot be generalised to other monkeys, it makes even less sense to extend these findings to human health outcomes.

Co-author Professor George Davey Smith, of the University of Bristol School of Social and Community Medicine, said:

" In the UK, systematic reviews are an essential requirement when used to informing decisions about human care, as NICE recommends. We should expect the same from studies in animals, and even more so when those studies are then applied to humans."

Health services researcher, Sir Iain Chalmers, one of the founders of the Cochrane Collaboration and coordinator of the James Lind Initiative, said:

" A thousand years ago Ibn Sina warned against incautious extrapolation from animal experiments to humans; yet, as the study by Petticrew and Davey Smith illustrates, this practice continues today. A recent increase in the numbers of systematic reviews of animal studies has begun to address this problem. As shown by Petticrew and Davey Smith here, these reviews have begun to reveal not only citation biases, but also important methodological deficiencies in many animal studies."

Ref. to Paper:
'The Monkey Puzzle: A Systematic Review of Studies of Stress, Social Hierarchies, and Heart Disease in Monkeys' by Mark Petticrew and George Davey Smith, in PLoS ONE online Ref: http://bit.ly/H2tm54.

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