Comparison of different methods of categorization for physical activity on coronary heart disease risk factors

Objective: There is a general agreement that physical activity (PA) has a beneficial effect<br/>on health and those who are more active have a reduced risk of developing many chronic<br/>diseases, such as coronary heart disease (CHD). However, the amount, type and intensity<br/>of PA deemed to be sufficient to achieve good health remains unclear. Different methods<br/>have been used to categorise activity behaviour, but the level of agreement, consistency<br/>and coherence between methods and how this might influence their relationship with CHD<br/>risk factors and estimated CHD (eCHD) risk are poorly understood. This uncertainty is<br/>reflected in many different messages communicated to the public as to how active they<br/>should be to prevent chronic diseases. The primary objective of this thesis was to<br/>determine whether the methods used to categorise PA (as either inactive/active or level of<br/>PA) influence the extent to which PA is associated with CHD risk factors and eCHD risk.<br/><br/>Methods: This thesis was divided into two parts. The first part was to conduct a<br/>secondary analysis of data on activity and CHD risk factors (blood pressure and lipid<br/>profile) obtained from the 2004 UK National Diet and Nutrition Survey (NDNS) in 1658<br/>adults aged 19-64 years. Using the information obtained from the NDNS 7-day diary, it<br/>was possible to extend the original observations and to re-categorise individuals according<br/>to measures of PA in terms of number of days and minutes of at least moderate PA, total<br/>activity expressed as metabolic-equivalents (METs) and self-perception of PA. Each of<br/>these methods was then used to examine the proportion of the variance in CHD risk<br/>factors and the eCHD risk attributable to differences in PA using General Linear<br/>Modelling with adjustment for BMI, age and smoking. Partial eta squared a “proportion of<br/>variance due to physical activity plus error that is attributed to physical activity alone” was<br/>used. In the second part, the concurrent validity of measures of PA derived from the<br/>NDNS 7-day diary, using different systems for coding and classifying of different physical<br/>activities, was compared against those measures of PA obtained from the International<br/>Physical Activity Questionnaire (IPAQ) in a group of medical students (n = 26).<br/><br/>Results: Taken together, this thesis revealed: 1) poor agreement across different methods<br/>of categorisation of PA level, 2) no support to justify a curvilinear dose-response<br/>relationship between PA level and CHD risk factors and eCHD risk and that a linear<br/>model was sufficient, 3) the differences in CHD risk factors or eCHD risk that could be<br/>directly attributable to differences in PA in men was modest (generally &lt; 5%) although no<br/>associations evident in the women, 4) effect was most obviously demonstrable as<br/>improvements in lipid profile, no demonstrable effect on blood pressure, 5) a potential<br/>problem might arise when using one system and applying its results to different guidelines<br/>established by different systems.<br/><br/>Conclusion: These findings support the view that being physically active is associated<br/>with markers of better health and lower CHD risk; a small but consistent effect that was<br/>the same irrespective of which method of categorizing PA was used and even after<br/>adjustment for differences in age, BMI and smoking. The effects were most evident in<br/>men and largely attributable to improvements in lipid metabolism.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Al-Haifi, Ahmad

Advisors dc:contributor.advisor

• Elia, Marinos
• Wootton, Steve