Title: Biochemical Measures of Nutritional Status
Key words: Biological markers, faecal, urine and blood analysis, contamination,
Date: Jan 1999
Category: 14. Measurement
Author: Dr van Rhijn
Various biological markers have been utilised as indicators of nutritional status because they give a predictive response to a given dietary component. They are also useful as independent validity checks in dietary surveys, as compared to direct measures of dietary intake, which are more prone to random errors. However, their usefulness as biochemical parameters depends on their sensitivity to fluctuations in dietary intake and robustness to interference from various external factors.
Biochemical markers for nutrients (tissue status) are generally subdivided into short term and medium to long term indices, according to their temporal relationships with dietary intake.
The main examples of biochemical analysis for each group are:
The strengths and weaknesses of the main individual indices are as follows:
Contamination of samples (metal needles, coated tubes, rubber stoppers etc) is a major source of error in biochemical assays and often neglected in validation studies. Detailed knowledge of the metabolism of nutrients is essential in order to select the most effective test which will provide the most valid reflection about its nutritional status.
Biological markers were primary developed to estimate the amount of nutrient present at tissue level rather than assuming a close relationship between measured laboratory levels and amounts present in the diet. They must be able to reflect relationships between diet, nutritional status and disease processes over a wide range of intakes. The validity of the data depends on numerous factors, which may influence test results. Fortunately, however, reference values for various nutrients are gradually becoming more readily available.
Bates C., et al. Biochemical markers of nutrient intake. Chapter 7 pp 170-240. In: Margetts B. & Nelson M. 1998; Design Concepts in Nutritional Epidemiology. Second Edition. Oxford University Press. New York.
Nelson M. The validation of dietary assessment. Chapter 8 pp 241-272. In: Margetts B. & Nelson M. 1998; Design Concepts in Nutritional Epidemiology. Second Edition. Oxford University Press. New York.
Bingham SA. The dietary assessment of individuals; methods, accuracy, new techniques and recommendations. Nutr Abst Rev 1987; 57: 705-742.
Hunter DJ. Biochemical indicators of dietary intake. Chapter 9 pp 143-216. In: Willit WC. 1990; Nutritional Epidemiology. Oxford University Press. New York.