Estimation of usual intake

Table V. Approximate Confidence Limits for the Estimation of Usual Intake Based Upon Various Numbers of One-Day Observations on One Individual ...

Traditionally, risk characterization is based on a deterministic approach, meaning that the risk is based on a point estimate, usually the worst-case value for each input variable (worst-case NOAELs, assessment factors, and exposure levels). This worst-case approach is intended to ensure that even the most sensitive part of the population is protected under all conditions, and therefore generally overestimates the health risk. In the case of food allergens, the maximum consumption of a food may be multiplied by the maximum concentration of the allergen in this food. This results in the maximum estimate of the intake of the allergen. If this intake is higher than the lowest threshold observed, a possible reaction to the allergen cannot be ruled out. 

Accurate assessment of supply and intake is a complex procedure. In practice, a crude estimate of intake can be obtained from a careful clinical history taken by an experienced practitioner or from a food frequency questionnaire that summarizes the content of the individuars diet over several days, depending on how frequently particular typical foods are consumed. A more accurate quantitative assessment usually requires a minimum of three days recording of a complete dietary diary, which is subsequently analyzed using a computer program with reference tables of the nutritional contents of most foods. Unfortunately, estimates of the portion size, amounts consumed, and actual nutritional composition of the food consumed may be inaccurate. In addition, the disease process also affects the amount actually consumed and absorbed, further reducing the accuracy of the estimate of nutritional intake. 

Later, JECFA proposed an alternative to TMDI, namely the estimated dietary intake (EDI), which has been accepted by the Australian authority. The difference from TMDI is the replacement of MRL by median residue concentration, on the reasonable consideration that, in the chronic intake circumstance, MRL does not provide a realistic estimate of residue intake. MRL is the upper limit of a high percentile (usually 95th) of the distribution of marker residue. In contrast, the median residue concentration provides the best point estimate of the central tendency over a prolonged period. 

As the number of days of observation increases, the total observed variance decreases. With an infinite number of days of observation, what would be seen would be the interindividual variation only. The distribution of usual intakes is estimated by the interindividual variation. It is the distribution of usual intakes that should be used in the probability analysis of population data. By appropriate statistical analyses, the interindividual variation can be estimated and the probability approach applied. To do this, it is not necessary to have a large number of observations on the intake of each individual. It is only necessary to have a sufficient number... 

If one wished to plot the distribution of usual intakes portrayed in Fig. 4 and had a knowledge of the points on the distribution portraying one-day intakes, as well as a separate estimate of the partitioning of variance, the following equation could be applied ... 

Monitoring the patient in shock requires vigilance on the part of the nurse The patient s heart rate, blood pressure, and ECG are monitored continuously. The urinary output is measured often (usually hourly), and an accurate intake and output is taken. Monitoring of central venous pressure via a central venous catheter will provide an estimation of the patient s fluid status. Sometimes additional hemodynamic monitoring is necessary with a pulmonary artery catheter. The use of a pulmonary artery catheter allows the nurse to monitor a number of parameters, such as cardiac output and peripheral vascular resistance The nurse adjusts therapy according to the primary health care provider s instructions. 

G A (2000) Assessing the accuracy of a food frequency questionnaire for estimating usual intake of phytoestrogens. Nutr Cancer. 37 (2) 145-54. 

In order to extrapolate laboratory animal results to humans, an interspecies dose conversion must be performed. Animals such as rodents have different physical dimensions, rates of intake (ingestion or inhalation), and lifespans from humans, and therefore are expected to respond differently to a specified dose level of any chemical. Estimation of equivalent human doses is usually performed by scaling laboratory doses according to observable species differences. Unfortunately, detailed quantitative data on the comparative pharmacokinetics of animals and humans are nonexistent, so that scaling methods remain approximate. In carcinogenic risk extrapolation, it is commonly assumed that the rate of response for mammals is proportional to internal surface area... 

Pharmacokinetics has played a crucial and somewhat unusual role in the assessment of health risks from methylmercury. Some of the epidemiology studies of this fish contaminant involved the measurement of mercury levels in the hair of pregnant women, and subsequent measurements of health outcomes in their offspring (Chapter 4). Various sets of pharmacokinetic data allowed estimation of the level of methylmercury intake through fish consumption (its only source) that gave rise to the measured levels in hair. In this way it was possible to identify the dose-response relationship in terms of intake, not hair level. Once the dose-response relationship was established in this way, the EPA was able to follow its usual procedure for establishing an RfD (which is 0.1 ag/(kg b.w. day)). 

An exposure assessment is the quantitative or qualitative evaluation of the amount of a substance that humans come into contact with and includes consideration of the intensity, frequency and duration of contact, the route of exposure (e.g., dermal, oral, or respiratory), rates (chemical intake or uptake rates), the resulting amount that actually crosses the boundary (a dose), and the amount absorbed (internal dose). Depending on the purpose of an exposure assessment, the numerical output may be an estimate of the intensity, rate, duration, and frequency of contact exposure or dose (the resulting amount that actually crosses the boundary). For risk assessments of chemical substances based on dose-response relationships, the output usually includes an estimate of dose (WHO/IPCS 1999). 

The values presented in Table 7.4 may possibly not be representative of long-term exposures as the duration of the studies was not sufficient in any of the studies in order to get a good estimate of the usual intake (sampling periods were between 3 and 8 days). The values presented in Table 7.4... 

Short period of sampling therefore the value is not an estimate for usual daily intake. ° Used for very short-term (acute) exposure. The value is based on a single pica child. 

Acceptable Daily Intake (ADI) The ADI of a chemical is the estimate of the amount of a substance in food and/or drinking water, expressed on a body weight basis, that can be ingested daily over a lifetime without appreciable health risk to the consumer on the basis of all of the known facts at the time of the evaluation. It is usually expressed in mg of the chemical per kg of body weight (EAO/WHO, 1997). 

Since the cancer potency and/or acceptable daily intake values are characteristics of the agent, they do not vary from situation to situation. Exposure, however, does. Exposure assessments provide an estimate of the dose to which individuals may be exposed via all possible routes in a specific circumstance. The result of the exposure assessment is usually expressed as a single number for example, the average daily dose. However, since no two individuals are likely to have the same exposure it may also be expressed as a distribution. This distribution provides estimates of the exposures of particular segments of the population for example, the top 95% of exposed individuals. 

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