segunda-feira, 11 de abril de 2011

Necessidades de água...

A água, como todos sabemos é um bem essencial para o nosso organismo!
Apesar de muitos dizerem, escreverem e pensarem que podemos reduzir o seu consumo, eu faço questão de contrariar esse pensamento.

Quando as questões são complexas, para mim é sempre fundamental procurar as respostas em locais crediveis.

Assim, ao lermos um dos relatórios da Organização Mundial de Saúde, verificamos que para manter o nosso nivel adequado de hidratação são necessárias grandes quantidades de água:
Requirements to maintain hydration
The evidence outlined above indicates that there are health concerns regarding hydration
status and therefore the requirements for human to maintain an adequate hydration level and
minimise risk of disease associated with adverse effects outlined above must be defined. The
definition of the ‘absolute minimum’ quantity of water to sustain hydration remains elusive,
as this is dependent on climate, activity level and diet.
In developing countries, White et al. (1972) and Gleick (1996) suggest that a minimum of 3
litres per capita per day is required for adults in most situations. However, households with
least access to water supplies are more likely to be engaged in at least moderate activity and
often in above-average temperatures. Data from the US Army reported in White et al. (1972)
provides estimates of water quantity needs at different temperatures and activity levels. This
indicates that at 25oC with moderate activity in the sun (for instance agricultural work)
approximately 4.5 litres are required to maintain hydration. This rises to about 6 litres at 30oC
or when hard work in the sun is undertaken at 25oC. Although the US Army has more recent
recommendations for hourly intake of water per hour in relation to heat categories and
activity intensity to prevent heat injury, this do not easily translate into non-military activity.
They do, however, stipulate that hourly fluid intake should not exceed 1.08 quarts (1.03
litres) and that daily intake should not exceed 12 quarts (11.35 litres) (United States Army
Center for Health Promotion and Preventive Medicine, 2003).
The literature reviewed in section 3.2 to 3.4, indicates that the quantity of water required for
hydration (whether via direct ingestion or food) should be a minimum of 2 litres for average
adults in average conditions, rising to 4.5 litres per day under conditions typically facing the
most vulnerable in tropical climates (see table 2 below) and higher in conditions of raised
temperature and/or excessive physical activity. This figure can be interpreted as applying to
all adults and to children, given the difficulty in determining whether the ration of adult/child
water requirements would remain the same with increasing activity and/or temperature. Thesevalues encompass the range in which beneficial impacts on prevention of coronary disease

and kidney stone occurrence appears likely and would be at the lower end of requirements to
prevent recurrence of kidney stones.
By also taking into consideration the needs of lactating women, many of whom in the group
with least access will still be expected to undertake moderate activity in high ambient
temperatures, a minimum quantity required of fluid required for hydration (via both direct
consumption and food) can be estimated as 5.5 litres per capita per day. This will not account
for those in unusually hot environments or engaged in strenuous physical activity where
minimum needs may be considerably greater.
As some hydration needs are met through fluid obtained from food, the figure of 5.5 could be
interpreted in two ways. Firstly, it could be assumed that the water supply should be able to
meet all hydration needs (i.e. minus contributions from food). The second approach would be
to assume that one-third of all hydration fluid is derived from food and that therefore
domestic water supply need only meet two-thirds of the minimum quantity identified.
In this report we use the former approach because as the proportion of fluid obtained from
food may vary significantly in response to diet and culture from negligible to all hydration
needs as noted by White et al. (1972). Therefore, trying to allocate a proportion of the fluid
requirement to food on a global basis would risk significantly under-estimating water
quantity needs in a number of situations where food contribution is negligible. As these are
likely to be found in situations with vulnerable populations, notably in emergencies, this
would entail a serious risk. Allocating the full hydration component to drinking water may
over-estimate the quantity of water required, but this is believed to be no more significant that
the variation likely to occur due to activity levels and temperature.

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