30 Koletzkoquirement of a nutrient is the intake sufficient to
meet the physiological requirement, considering
nutrient bioavailability from foodstuffs. NIV re-
f lect the estimated distributions of nutrient in-
takes required to achieve a specific outcome in a
defined population considered healthy, but for
ma ny nut r ients, t h is d ist r ibut ion of requ i rements
and the modifying biological and environmental
factors are not well known, which results in con-
siderable uncertainty regarding NIV. Therefore,
NIV should be considered approximations that
ref lect the often limited data available. NIV are
even more uncertain for infants and young chil-
dren, on whom original data are particularly
scarce, and, hence, NIV are often derived from
the interpolation of data from other age groups,
which must be expected to yield inaccurate val-
ues. It is important to remember that NIV refer
to populations but not to individuals. NIV do not
allow us to determine an insufficient nutrient in-
take or a nutrient deficiency in an individual, or
to accurately determine nutrient needs in disease
states.
Definitions of NIV
NIV for populations are generally estimated
based on the concept that individual require-
ments follow a statistically normal distribution
(bell-shaped curve in fig. 1 ). The average nutrient
requirement (ANR; also called ‘estimated average
requirement’) is the estimated average of the
median requirement of a specific nutrient in the
population derived from a statistical distribution
of requirement criterion and for a particular age-
and sex-specific group based on a specific biolog-
ical end point or biochemical measure. The popu-
lation reference intake (PRI; also called ‘individ-
ual nutrient level 97%’, ‘reference nutrient intake’
or RDA) is the nutrient intake considered ade-
quate to meet the known nutrient needs of practi-
cally all healthy individuals in a particular age-
and sex-specific group. Based on the assumed sta-
tistical distribution of requirements, the PRI is set
at a level of intake that meets the needs of 97% of
the population (mean + 2 SD) ( fig. 1 ). The PRI
value is generally used as the target for provision
of essential nutrients to populations and as the
reference point for the nutrient labelling of foods,
with the exception of energy, where the ANR is
used because the provision of energy equivalent
to the PRI would result in overfeeding and induc-
tion of obesity in about one half of the population.
The upper nutrient level (UNL; or upper tolerable
intake level) is the highest level of daily nutrient
intake that is likely to pose no risk of adverse
health effects for almost all individuals of a par-
ticular age- and sex-specific group. Ideally, the
UNL is based on an analysis of the statistical dis-
tribution of risk for high nutrient intakes. The
UNL is generally set at a level where the risk of
excessive intake is practically non-existent. A nu-
trient intake equal to or higher than the UNL
should be avoided on a chronic basis.
Examples of NIV for children and adolescents
are provided in Annex 4.3.Limitations to the Estimation of NIVThe concept of a near-normal, symmetrical dis-
tribution of nutrient requirements ( fig. 1 ) is
known not to be correct for a number of nutri-
ents. Examples are the nutrient needs for iron,
vitamin D and polyunsaturated fatty acids. Iron
requirements are not normally distributed, with
high needs in menstruating women, particularly
in those with substantial blood losses. Vitamin D
requirements depend on endogenous synthesis in
the skin and hence on variation of UV light expo-
sure with geographic location and the time of the
year, as well as on biological determinants such as
the degree of skin pigmentation and genetic vari-
ations in the vitamin D receptor. The dietary
needs of essential fatty acids vary considerably
with genetic polymorphisms for the fatty acid de-
saturation enzymes Δ^6 and Δ^5 desaturases thatKoletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 29–33
DOI: 10.1159/000369234