Variability in Micronutrient Requirements among Individuals

Professor RJ Williams, a chemist who played a key role in the discoveries of pantothenic acid and folic acid, emphasized the broad variability in micronutrient needs within the population. He developed the concept of "biochemical individuality," a fundamental principle of micronutrient prevention and therapy, describing it as follows:

"Each individual has a distinctive nutrient environment of his or her own, because while the list of nutrients needed by all of us may be the same, the respective amounts needed are necessarily not the same for all individuals.24"

Put simply, each person has unique nutritional requirements. Depending on one's individual genetic makeup, striking variability can exist in the body's biochemistry. A nutrient intake sufficient for one person may be inadequate for another. For example, 2 mg/day of vitamin B6 is adequate for good health in most people, yet some individuals with inherited defects in vitamin B6 metabolism need up to 30 to 100 times this amount.25 The absorption and daily requirement for calcium can vary four- to fivefold among healthy middle-aged women.26 Normal plasma concentrations for 1,25 (OH)2 vitamin D (the activated form of the vitamin) vary between 15 and 45 pg/ml in healthy adults.9 In the 10% of the population who are heterozygous for the hemochromatosis gene (see pp. 68), dietary iron intakes that normally maintain health may be toxic in the long-term.27

Biochemical individuality also helps explain why different people react differently to dietary factors. For example, a high intake of salt will increase blood pressure in the one-third of the adult population who are "salt-sensi-tive,"28 while others simply excrete the excess without ill effects. A high amount of dietary cholesterol may produce hypercholesterole-mia in some people, but not all.29

Moreover, besides these genetic differences, nutritional requirements can be profoundly influenced by many factors, including age, environment, and lifestyle choices. A smoker's requirement for vitamin C is two to three times that of a nonsmoker.30 Pregnancy doubles a woman's need for iron. Strenuous athletic training sharply increases requirements for the vitamin B complex and magne-sium.31 Therefore, across the population, there a broad range of optimum intakes for the essential nutrients. Factors which cause nutritional needs to vary from person to person are shown in the table below and are considered in detail in later sections.

Factorsthat cause nutritional needs to vary from person to person

• Genetic differences

• Growth during child

(biochemical indi

hood and adoles

viduality)

cence, aging

• Pregnancy and

• Gender

breastfeeding

• Illness, infection, or

• Regular alcohol or

surgery

caffeine intake

• Smoking

• Dietary factors, levels

of intake forfat, car-

bohydrates, fiber, and

protein

• Drug-nutrient inter-

• Exposure to environ-

actions

mental pollutants

• Psychological and

• Activity and exercise

emotional stress

level

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