Here is the design of a clinical trial:

Official Title: Effect of High Cocoa Content Chocolate on Vascular Function, Body Composition, Health-related Quality of Life and Cognitive Performance in Postmenopausal Women.

Included conditions:
- Postmenopausal Women

Study Armgroups:
- {'label': 'Control group', 'type': 'NO_INTERVENTION', 'description': 'No intervention'}
- {'label': 'Intervention group', 'type': 'EXPERIMENTAL', 'description': 'Addition of 10 g/day of high cocoa content chocolate to the usual diet for six months', 'interventionNames': ['Dietary Supplement: Intervention group']}

Interventions:
- {'type': 'DIETARY_SUPPLEMENT', 'name': 'Intervention group', 'description': '10 g/day of high cocoa content chocolate for six months.', 'armGroupLabels': ['Intervention group']}

Primary Outcomes:
- {'measure': 'Blood pressure', 'description': 'Measurement by oscillometric method (mmHg)', 'timeFrame': '6 months'}

Please estimate the sample size based on the assumption: 
Alpha risk of 0.05, beta risk of 0.20, standard deviation (SD) of 5.8 mm Hg, and a predicted drop-out rate of 10%.
Sample size
        The size of the sample has been estimated based on the potential modification of the main variable, systolic blood pressure (SBP). Given alpha and beta risks of 0.05 and 0.20 respectively in bilateral contrast and an SD of 5.8âmmÂ Hg, 140 participants (70 per group) will be necessary to detect a minimum difference of 2.9âmmÂ Hg in the SBP between the two groups. A predicted drop-out rate of 10% during follow-up has been taken into account. This estimate has considered the results obtained in a similar study in which a decrease in SBP of 6.5 was observed Â±5.8âmm Hg.14