How reliable are commercially available trackers in detecting daytime sleep

Polysomnography (PSG) is still regarded as the gold standard in determining sleep patterns. However, PSG is complicated, burdensome and the hospital set‐up of PSG has the disadvantage of not being able to measure sleep over a long period 1, 2, 3, 4. An alternative way to measure sleep is with actigraphy. Actigraphs use the 24‐h movement of a person to assess the wake–sleep rhythm. Actigraphy is not a direct measurement of sleep, but is a convenient alternative method to determine someone's sleep patterns. There are professional‐level actigraphs that already have been validated in published studies 1, 3, 5, 6, 7.

The use of new consumer‐grade wearable actigraphy trackers to evaluate sleep patterns is increasing in clinical research 2, 4, 8, 9, 10, 11, 12, 13. These trackers are able to measure sleep patterns with the same precision as professional medical‐grade actigraphy wristbands 2, 4, 10, 11, 13. Actigraphy can be used to measure the pharmacological impact of drug trials on circadian rhythm and sleep patterns objectively. Actigraphy trackers are also used in paediatric research, because they can contribute in monitoring sleep patterns of children in clinical studies during real‐life conditions. Sleep patterns can be monitored in children with sleep disorders with low burden over multiple days with wearable trackers instead of one overnight screening with PSG. Paediatric studies generally assess standard variables such as age, sex and ethnicity that are influencing sleep behaviour, when sleep patterns are measured with trackers or PSG 2, 4. However, these studies do not mention something infants and young children regularly do: daytime napping.

It is common for children up to age 6 years to have naps during the day 14. Children, who take daytime naps, have a shorter sleep time during the night, but children taking daytime naps have in general the same sleep duration as children without daytime naps 14. Therefore, it is important to take these sleeping habits into account when investigating the total sleep duration of young children. A literature search revealed only one study 15 that investigated the effect of these naps on the total sleep time using professional‐grade actigraphy. Another study with PSG and a consumer‐available tracker reported daytime napping only in an additional paper diary 6. However, no mention was made of whether daytime napping was included in the measurements. If sleep patterns are used to investigate the pharmacological effect of a drug in paediatric clinical studies, then napping time should be accounted for in the study design. Reported demographics should furthermore include information on whether the child is prone to daytime sleep aside from the standard variables. Populations such as young children, but also older people and shift workers, are prone to daytime sleep and thus actigraphy trackers should be validated for the assessment of daytime naps. The study design of clinical research with trackers should define sleep thoroughly. The study design should also take into account whether the specific type of tracker used is even able to detect daytime sleep 16.

This letter to the Editor aims to increase awareness of readers to be critical of clinical studies that use trackers or PSG to determine the clinical or pharmacological outcome of sleep pattern measurements. Besides standard demographic variables, the definition of sleep and individual sleeping habits should be considered. Therefore, it should be mentioned in an article how sleep is defined and measured, and which activity trackers are used to measure sleep. Daytime sleep could prove an important factor besides night‐time sleep and other variables of sleep activity.

Competing Interests

There are no competing interests to declare.

Lambrechtse, P. , Ziesenitz, V. C. , Cohen, A. , van den Anker, J. N. , and Bos, E. J. (2018) How reliable are commercially available trackers in detecting daytime sleep. Br J Clin Pharmacol, 84: 605–606. doi: 10.1111/bcp.13475.