The Apple Watch for Monitoring Mental Health Related Physiological Symptoms: A Literature Review (Preprint)

BACKGROUND An anticipated surge in mental health service demand related to COVID-19 has motivated the use of novel methods-of-care to meet demand given workforce limitations. Digital health technologies in the form of self-tracking technology have been identified as a potential avenue, provided sufficient evidence exists to support its effectiveness in mental health contexts. OBJECTIVE The objective of this literature review is to identify physiological monitoring capabilities of the Apple Watch relevant to mental health monitoring, to examine the accuracy and validation status of these measures, and the implications of these measurements on mental health treatment. METHODS A literature review was conducted in June-July 2021 for both published and grey literature pertaining to Apple Watch, mental health and physiology. The literature review identified studies validating sensor capabilities of the Apple Watch. RESULTS A total of 5,583 paper titles were identified, with 115 papers reviewed in full. Of these, 19 papers were related to Apple Watch validation or comparison studies. Most studies showed the Apple Watch to measure heart rate acceptably with increased errors in case of movement. Accurate energy expenditure measurements are difficult for most wearables, with Apple Watch generally providing best results compared to peers, despite overestimation. Heart Rate Variability measurements were found to have gaps in data, but was able to detect mild mental stress. Activity monitoring with step counting shows good agreement, although wheelchair use was found to be prone to overestimation and poor performance on overground tasks. Atrial Fibrillation detection showed mixed results in part due to a high inconclusive result rate but may be useful for ongoing monitoring. No studies recorded validation of the Sleep app feature, however, accelerometer-based sleep monitoring showed high accuracy and sensitivity in detecting sleep. CONCLUSIONS The results are encouraging regarding the application of Apple Watch in mental health, particularly as heart rate variability is a key indicator of changes in both physical and emotional states. Particular benefit may be derived through avoidance of recall bias and collection of supporting ecological context data. However, a lack of methodologically robust and replicated evidence of user benefit, supportive health economic analysis and concerns around personal health information remain key factors that must be addressed to enable broader uptake.