Methods: An umbrella review of the evidence across systematic reviews and narrative reviews of endogenous and exogenous (supplementation) MLT was undertaken. The Oxman checklist for assessing the methodological quality of the included SRs was utilised. The following databases were searched: MEDLINE, EMBASE, Web of Science, CENTRAL, PsycINFO, and CINAHL as well as screening of reference lists. We included reviews of the effects of MLT on any type of health-related outcome measures.
Results: One hundred and ninety-five reviews met the inclusion criteria. Most were of low methodological quality (mean=-4.5, standard deviation=6.7). Of those, 164 did not pool the data and were synthesised narratively (qualitatively) whereas the remaining 31 used meta-analytic techniques and were synthesised quantitatively. Seven meta-analyses were significant with P values less than 0.001 under the random-effects model. These pertained to sleep latency, pre-operative anxiety, prevention of agitation, and risk of breast cancer.
Conclusions: There is an abundance of reviews evaluating the effects of exogenous and endogenous MLT on health. In general, MLT has been shown to be associated with a wide variety of health outcomes in clinically and methodologically heterogeneous populations. Many reviews stressed the need for more high quality randomised clinical trials to reduce the existing uncertainties.
- systematic reviews