An apparatus for determining for a user a correlation between an overnight glucose level change as a function of activity, comprising: a data input interface for receiving activity level information of the user and glucose level information of the user over a predetermined time period, the predetermined time period including a first time period and a second time period; a data analysis module (110B, 112) operatively coupled to the data input interface, and configured to: categorize the first time period to include overnight glucose level information for days within the predetermined time period with significant activity, and the second time period to include overnight glucose level information for days within the predetermined time period without significant activity; determine a correlation for the user between the overnight glucose level information for the first time period and the overnight glucose level information for the second time period, the correlation being as a function of the activity; and determine for the user, based on the determined correlation, the impact on overnight glucose level based on a measured level of activity of the user; and a data output interface (110B, 113) operatively coupled to the data analysis module (110B, 112) to output information associated with the determined impact on the overnight glucose level. a data input interface for receiving activity level information of the user and glucose level information of the user over a predetermined time period, the predetermined time period including a first time period and a second time period; a data analysis module (110B, 112) operatively coupled to the data input interface, and configured to: categorize the first time period to include overnight glucose level information for days within the predetermined time period with significant activity, and the second time period to include overnight glucose level information for days within the predetermined time period without significant activity; determine a correlation for the user between the overnight glucose level information for the first time period and the overnight glucose level information for the second time period, the correlation being as a function of the activity; and determine for the user, based on the determined correlation, the impact on overnight glucose level based on a measured level of activity of the user; and categorize the first time period to include overnight glucose level information for days within the predetermined time period with significant activity, and the second time period to include overnight glucose level information for days within the predetermined time period without significant activity; determine a correlation for the user between the overnight glucose level information for the first time period and the overnight glucose level information for the second time period, the correlation being as a function of the activity; and determine for the user, based on the determined correlation, the impact on overnight glucose level based on a measured level of activity of the user; and a data output interface (110B, 113) operatively coupled to the data analysis module (110B, 112) to output information associated with the determined impact on the overnight glucose level.