Abstract: We examined 5384 abstracts and identified 21 studies as potentially eligible. Following a full text analysis, we included 14 papers reporting results of 7 clinical studies (2 papers report on the same trial) and 6 analogue studies. Of the seven clinical studies, five assessed smoking cessation. Meta-analyses revealed no statistically significant effects on either short-term (less than 6 months) smoking cessation (OR 1.35, 95% CI 0.76 to 2.39, P = 0.31, n = 3 studies) or cessation after six months (OR 1.07, 95% CI 0.64 to 1.78, P = 0.80, n = 4 studies). Two clinical studies assessed diet and found effects that significantly favoured DNA-based risk estimates (OR 2.24, 95% CI 1.17 to 4.27, P = 0.01). No statistically significant effects were found in the two studies assessing physical activity (OR 1.03, 95% CI 0.59 to 1.80, P = 0.92) or the one study assessing medication or vitamin use aimed at reducing disease risks (OR 1.26, 95% CI 0.58 to 2.72, P = 0.56). For the six non-clinical analogue studies, meta-analysis revealed a statistically significant effect of DNA-based risk on intention to change behaviour (SMD 0.16, 95% CI 0.04 to 0.29, P = 0.01). There was no evidence that communicating DNA-based disease risk estimates had any unintended adverse effects. Two studies that assessed fear arousal immediately after the presentation of risk information did, however, report greater fear arousal in the DNA-based disease risk estimate groups compared to comparison groups. The quality of included studies was generally poor. None of the clinical or analogue studies were considered to have a low risk of bias, due to either a lack of clarity in reporting, or where details were reported, evidence of a failure to sufficiently safeguard against the risk of bias. Mindful of the weak evidence based on a small number of studies of limited quality, the results of this review suggest that communicating DNA-based disease risk estimates has little or no effect on smoking and physical activity. It may have a small effect on self-reported diet and on intentions to change behaviour. Claims that receiving DNA-based test results motivates people to change their behaviour are not supported by evidence. Larger and better-quality RCTs are needed.

Plain-language summary: Five clinical studies assessed smoking cessation, with statistical combination of the results revealing no statistically significant effects on smoking cessation in either the short-term (< six months) or long term (> six months). Two clinical studies assessed dietary behaviour and showed that communicating genetic test-based risk estimates did change people's behaviour.The two studies assessing physical activity and the one study assessing medication or vitamin use aimed at reducing disease risks did not show that communicating DNA-based disease risk estimates had an effect on behaviour. For the six analogue studies, statistical combination of the results revealed a statistically significant effect of genetic test based disease risk estimates on intention to change behaviour only. There was no evidence of any unintended detrimental effects on motivation or mood. In summary, the limited amount and quality of evidence currently available suggests that communicating genetic test based disease risk estimates may have little or no effect on behaviour, but may have a small effect on intentions to change behaviour. Larger and better quality trials are needed.