1. Brief definitions of the study design, sampling strategy, and outcome variable(s)

Study design: cross sectional study is carried out at just one point in time or over a short period of time. It provides estimates of the features of a community at just one point in time and they are suitable for measuring prevalence. A cross-sectional survey conducted during June-August 2009 in South East Qld.

Sampling strategy: random sampling defines when the required number of individuals selected at a random from the sampling frame, a list or a database of all individuals in the population. In this study sample included random selection of healthy men and women aged 50-85 years; subject were free from any condition likely to impact on Vitamin D status or calcium/bone metabolism (potential comorbidities). In this study, a number of 789 had completed a self-administered questionnaire (including self-reported typical sun exposure), a 14-day food diary and provided a fasting blood plasma sample to assess 25-hydroxyvitamin D [25(OH) D].

Outcome variables: Outcome variables are usually the dependent variables. These values usually presented as means or frequencies/percentages by group (e.g., Prevalence of individuals with vitamin D insufficiency) and are often the content of cells in tables and on the Y-axis of graphs. In this study the outcome variable is vitamin D status which was assessed by measuring 25 hydroxyvitamin D [25 (OH) D] concentrations in fasting EDTA -plasma, measured in nmol/L. Vitamin D insufficiency was considered as a serum 25 (OH) D <50nmol/L.