Scientific Concept of the National Cohort (status ... - Nationale Kohorte

Physical activity
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A.3 Study design
Physical activity is a complex behavior that can be subdivided into type of activity, frequency,
duration, intensity, and setting. The true effect of physical activity on health outcomes
is likely to be underestimated due to substantial measurement error in the existing assessments
of physical activity, and the exact contribution of the different components of physical
activity to chronic disease is unclear532 . Most previously conducted studies have only used
questionnaires to assess physical activity, most of them aiming to estimate energy expenditure.
However, there is wide agreement that the validity of existing physical activity ques-
tionnaires is limited for estimating energy expenditure and quantifying physical activity
238, 240,
533 . Therefore, the main instrument for measuring physical activity will rely on accelerometry,
which is an objective measure, while supplementary information on activity patterns will be
obtained by questionnaire. The combination of monitoring physical activity via web-based
physical activity recalls and simultaneous measurement of physical activity by an objective
device (triaxial accelerometer) is needed to improve the precision of physical activity data.
Instruments:
The physical activity questionnaire for the National Cohort will address those aspects of
physical activity that are not covered by objective measurement devices such as accelerometers.
Information on physical activity will be obtained for the past 12 months. Thus,
seasonal variation in physical activity can be analyzed, which would not be possible with the
short-term accelerometric physical activity assessment. The aim of the questionnaire is to
assess the activity behavior and structural and temporal patterns (whereas energy expenditure
will be estimated by an objective device). Therefore, based on experience from existing,
validated questionnaires, a new-generation questionnaire has been developed and is
currently being tested in a substudy in EPIC-Germany.
In addition, a computer-based physical activity recall (CPAR-24) will be used to obtain more
detailed information on all physical activities undertaken during the previous 24 hours. This
information is necessary to derive algorithms for interpreting the accelerometer data.
diet
Diet has been hypothesized to play an important role in the development of major chronic
conditions, such as CVD, diabetes, cancer, and osteoporosis. Such hypotheses are based
on an abundance of plausible biological mechanisms relating diet and nutrition to disease
occurrence. To date, however, nutritional epidemiologic studies have not generated thoroughly
consistent evidence regarding the role of many dietary factors in disease etiology.
Thus, several hypotheses on associations between dietary factors and disease occurrence
remain to be clarified 239 .
One possible explanation for the inconsistency in previous nutritional epidemiologic studies
of chronic diseases is the methodological challenge in validly assessing habitual diet
in free-living individuals. There is particular concern that dietary assessment instruments
commonly used in large-scale studies (food frequency questionnaire) are prone to substantial
measurement error, which might have resulted in considerable underestimation of
true associations 534 . Therefore, improved instruments of data collection will be used in the
National Cohort.
Instruments:
Recent advances have rendered the use of multiple, internet-based 24-h dietary recalls
possible, implemented in combination with a food list (for identification on nonconsumers of
A.3