lipids & CVD

• risk factor: any factor that increases the chance of developing a particular condition or disease
• an increase in a risk factor doesn't guarantee the development of disease but increases the risk e.g increased blood cholesterol is a risk factor for incidence of CVD
• • an increase in the presence of a risk factor would be expected to lead to increased incidence of disease
  • the incidence of disease describes the number of cases of a disease that occur within a particular group of people within a given time
• cholesterol

  • type of lipid produced in the body
  • used for cell membrane functioning, sex hormone structure, bile synthesis
• cholesterol transported around the body as lipoproteins

  • lipoproteins are molecules composed of lipid and protein
  • two types are HDLs and LDLs
• HDL

  • contains unsaturated fat, cholesterol, protein
  • these molecules transport cholesterol from body tissues to the liver to be recycled or excreted; responsible for reducing blood cholesterol levels when it is too high
  • contribute to removal of cholesterol from fatty plaques that form during atherosclerosis
• LDL

  • contain saturated fat, cholesterol, protein
  • moves cholesterol from liver into bloodstream where it remains until it is required by cells; they increase blood cholesterol levels when it is too low
• LDL

  • binds to receptors on cell surface membranes, enabling them to be taken up by the cells that need them and removing cholesterol from the blood
  • high levels of LDL can lead to blockage of these membrane receptors, causing blood cholesterol to rise
• • when your body has too much LDL cholesterol the membrane receptors on the surface of cells are blocked, leading to an overall rise in blood cholesterol
  • cholesterol contributes to the formation of plaques in the arteries
• HDLs carry cholesterol to the liver where it is broken down and excreted, therefore lowering overall blood cholesterol levels
• the healthy ratio of LDL:HDL is roughly 3:1

  LDL:HDL ratio larger than 5:1 increases risk of heart disease
• sample size: a study with a large sample size will give results that are more likely to be representative of the target population
• individuals in the sample: the results of a study can only be applied to parts of the population represented in the sample

  e.g if the sample only contains women aged 20-40 then the results cannot be used to draw conclusions about the effect of smoking on males or older women
• control group; a study of this nature needs to contain a control group so that the effects of the variable of interest can be isolated from the effects of other factors
• control group

  • in this example the control group would contain individuals who do not smoke; this gives a baseline against which the results from the smoker group can be compared
  • all factors other than the variable of interest should be controlled between the control group and the test group e.g age diet activity levels
• statistical significance; the differences between groups need to be sufficiently large to be sure that they are not just the result of random chance
• • if standard deviations overlap then the difference between data sets is not statistically significant
  • if the standard deviations do not overlap then the difference is statistically significant
• the influence of other variables; variables other than the variable of interest need to be controlled so that they do not impact the results; in this study such control variables may include genetics, secondary exposure to smoking, exercise levels and diet
• describe the relationship shown in the graph

  • number of deaths increases as LDL blood conc. increases
  • number of deaths decreases as LDL blood conc. increases above 190
• comment on the validity of this conclusion

  • not valid
  • as study was only carried out on males/people aged 25-40
  • therefore cannot apply results to females/other age groups
  • the deaths may have been caused by other factors
  • no idea of sample size/duration of the study