How are RDAs decided?
Deciding on a Recommended Daily Allowance of a nutrient is not a straight-forward undertaking. The decisions are based on careful assessments of the amount of nutrient required to prevent a deficiency, often with the aid of a biochemical indicator of the extent of the deficiency.
The values obtained can be used for authorities to give nutritional advice. However, it cannot provide much help if the requirements of an individual are affected by variants of genes that affect how the micronutrient is used, such as in the case of folate.
An independent insight into whether normal levels of micronutrient in serum are adequate is to determine whether chromosomes are being fully maintained using a test carried out on blood cells.
Microscopy is used to detect whole or fragmented chromosomes that fail to separate with the unaffected chromosomes during a nuclear division. This method has provided evidence of the serum levels of micronutrient needed to prevent genomic damage by deficiencies of vitamins B3, B6, B7, B9, B12, and C, iron, magnesium, zinc, choline, selenium, copper and calcium.
A comparable stratagem is to use a test to measure the effect of micronutrient deficiency on mitochondrial function. Such tests indicate the optimum amount of a micronutrient to ensure proper maintenance of the genome or a functional mitochondrion; this is likely to be enough to maximise the healthy life span and is probably much more than the amount needed to prevent acute disease.
Determining the levels of essential fatty acids that should be present in a diet has always been a perplexing problem. Recently the focus for making dietary recommendations has shifted towards the levels needed for prevention and treatment of cardiovascular disease as it is clear from surveys that subjects who had the highest consumption of alpha linolenic acid had the lowest chance of a heart attack. Substantial protection was obtained with 0.58 g per day of alpha linolenic acid but potentially greater benefits were achievable with 2.8 g per day.