Normal biological variation

Such effects may be confused or obscured by normal biological variation, as they are typically only 30% to 60% above the control. Furthermore, if the background level of tumor incidence (or other effect being measured) is low, it may be impossible to assess hormesis. 

In the UK the Joint Food Science and Safety Group of the Department of Health and the Ministry of Agriculture, Fisheries and Food have published the results of many analyses for chemical contaminants in food carried out under their Food Surveillance Programme. In many cases the raw data from these surveys are available for analysis. Table 2.1 lists the results of analyses for lead in some samples of cow, sheep and pig kidney obtained in Scotland and England.5 There are clear differences between species and some evidence of differences between sampling locations. What is not clear is the extent to which the variability observed is due to real and consistent differences between species and location or to normal biological variation. 

In designing studies and before the interpretation of data, it is important to consider some of the variables that can affect the data but are unrelated to the compound being tested because changes can occur in plasma and urine values due to normal biological variations. In addition to biological variations, other variations may be caused by analytical variation and the methodological variation that occurs when a study is performed. 

Biomarkers discovery is one of the most difficult tasks in biology partly due to the level of complexity of biological systems. To start with there are the problems of normal biological variation of 10-40%. This type of variation is impossible to reduce or eliminate from an experiment and thus must be accounted for in the statistical analysis. This variation arises from the differences in individuals resulting... 

For blood at 37 C, the normal mean value is p/C P) = 6.103, with a normal biological standard deviation (SD) of about 0,0015, mainly caused by variations in ionic strength. The solubility coefficient for CO2 gas, a, also varies with the composition of the solution. For pure water at 37 °C, the solubility coefficient a = 0.0329 mmol x L x mmHg , and for normal plasma at 37 °C it is 0.0306 mmol x L X mmHg", with a biological SD of about 0.0003 mmol x L X mmHg ... 

Shurubor, Y.I. et al., Analytical precision, biological variation, and mathematical normalization in high data density metabolomics, Metabolomics, 1(1), 75, 2005. 

When proteins are heated above body temperature or when they are subjected to unusual acid or base conditions or treated with special reagents called denaturants, they lose some or all of their tertiary and secondary structure. Called denatured proteins, proteins in this state no longer exhibit normal biological activities. Figure 22.14 shows the variation of rate with temperature for a typical enzyme-catalyzed reaction. 

CoTLQVE E, Harris EK, Williams G (1970) Biological and analytic components of variation in long-term studies of serum constituents in normal subjects. Physiological and medical imph-cations. Clin Chem 16 1028-1032. 

The normal range of variation of each Hp type is remarkable. It is wider than what is usually found for substances of biological importance and is of the magnitude generally found for substances in transport. From the wide range of variation it is reasonable to assume that no such feedback mechanism exists and that the rate of Hp synthesis is influenced, directly or indirectly, by the plasma level. 

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