OBJECTIVES: Determine the prevalence of Vitamin D insufficiency during a Queensland (Qld) winter (June-August 2010).
Identify the determinants of Vitamin D status in an older ambulatory population residing in South East Queensland, and provide someindication of their relative importance to serum 25- Hydroxyvitamin D levels [25 (OH) D].
RATIONALE: Vitamin D plays an essential role in bone metabolism, maintaining bone health, as well as muscle function. Evidence suggests the long term impact of insufficient Vitamin D on calcium absorption may be associated with the development of conditions such as osteoporosis, and an increase in rates of falls and fractures. Other evidence suggests Vitamin D deficiency may be linked with autoimmune diseases, hypertension and various cancers.
Almost all Vitamin D is manufactured in the skin following direct exposure to sunlight (UV-B sunlight). The amount produced will depend on various factors such as the duration of sun exposure, season, and skin colour. Various sun protection practices can also impact on the manufacture of Vitamin D in the skin.
Small amounts of Vitamin D can be derived from dietary sources with major food sources including Vitamin D-fortified dairy products, egg yolks, liver, oily fish and fish oils. Some calcium supplements and most multivitamins contain vitamin D.
The ability to make vitamin D through the skin decreases with age and is lower in those with darker skin compared to those with a fair complexion. People who are housebound and/or experience no sunlight exposure are unable to make vitamin D.
The important role of Vitamin D in maintaining healthy bones and muscle strength is well established; however Vitamin D deficiency may pose health consequences that have yet to be fully appreciated. Maintaining adequate levels of 25 (OH) D throughout the lifespan may help to the reduce risk of various chronic illnesses. Understanding the range of factors that impact on Vitamin D status, particularly during the winter months, has important public health implications.
STUDY DESIGN: A cross-sectional survey was conducted during June-August 2009, to (1) determine the prevalence of Vitamin D insufficiency, and (2) identify the determinants of Vitamin D Status in an older population.
Your analytical plan should provide a complete, unambiguous ‘recipe’ of how to approach the analysis and reporting of the study – the following headings are suggestions for structuring your plan and to help you address the task in a systematic way.
Feel free to add more subheadings to your plan, or to change the order if it fits better with the approach you wish to take:
1) A statement of the scientific hypothesis/hypotheses you have decided to address in your analyses, with a rationale for each.
2) Brief definitions of the study design, sampling strategy, and outcome variable(s)
3) Strategies for data cleaning and checking consistency of problem responses in the given dataset
4) Comment on influence of study design, sampling strategy and scale of measurement of outcome variable, on your choice of analytical approach.
5) Rationale for choice of any exploratory analytical approaches
6) Rationale for choice of any modelling approaches (both statistical method, and model building approach)
7) List of specific models to be fitted and what problem you expect to answer with each
8) Assumptions to be tested for each analytical approach [and suggested alternative strategies if assumptions are not met]
9) Criteria that will be used for reporting significant associations
10) Dummy tables and/or graphs depicting the style of presentation of results from your proposed analyses. Remember that the format (headings and presentation) must be planned to a high level of reader-friendliness for the report.