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A asma, a obesidade e a hormona vitamina D - A hipĆ³tese do sol
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Authors
Advisor(s)
Abstract(s)
A conhecida āhipĆ³tese da higieneā,
segundo a qual a reduĆ§Ć£o das doenƧas
infecciosas leva ao aumento das doenƧas
atĆ³picas, foi explicada pelo desequilĆbrio
da actividade das linhas TH1 e TH2
a favor da Ćŗltima, uma vez que a activaĆ§Ć£o
da primeira se relaciona com a defesa
Ć infecĆ§Ć£o e a auto-imunidade, e a
segunda com doenƧas atĆ³picas. Mas o
aumento simultĆ¢neo da prevalĆŖncia de
doenƧas auto-imunes e atĆ³picas obrigou
a encontrar outra explicaĆ§Ć£o, admitindo-se
a existĆŖncia de cĆ©lulas T reguladoras
(Tregs) da actividade das duas linhas,
activadas por componentes infecciosos
como enterotoxinas. Mas as Tregs tĆŖm
receptores para a vitamina D, capazes de
serem estimulados. E como se tem vindo
a demonstrar uma carĆŖncia planetĆ”ria em
vitamina D, pode aventar-se outra hipĆ³tese
para explicar a maior prevalĆŖncia das
doenƧas atĆ³picas e auto-imunes, a hipĆ³tese
do sol. Simultaneamente, a carĆŖncia
de sol (isto Ć©, vitamina D) pode explicar o
aumento e /ou gravidade de outras patologias,
pois hĆ” receptores para a vitamina
D em variadas cĆ©lulas, que nĆ£o enterĆ³citos,
cƩlulas tubulares renais e osteoblastos,
e de correlaƧƵes patolĆ³gicas, como
asma e obesidade. ABSTRACT
The hygiene hypothesis was developed
to explain the increased prevalence
of atopic diseases in the last decades,
specialy in industrialized/developed
countries. The central core of the hypothesis
is that reduction in exposure to infectious
disease and microbial products
(through the introduction of vaccines,
antibiotics, and improved sanitation) has
resulted in deficient immune regulation
resulting in hypersensitivity in both the T-helper type 1 (Th1) and T-helper type 2
(Th2) compartments (The Th1 pathway
is characterized by the cell mediated
proinflamatory responses and is also involved
in certain autoimmune diseases;
the Th2 pathway is envolved in production
of immunoglobulin E, eosinophilia,
atopy and airway hyperresponsiveness).
However, the simultaneous increasing
prevalence of autoimmune diseases led
to the review of the scientific support of
the hypothesis, introducing the role of Tregulatory
cells (Tregs), up regulated by
infectious components like enterotoxins.
This up regulation can also be effectuated
by vitamin D, as Tregs have receptors
for this vitamin. Since now we assist
to an epidemic deficiency of vitamin D, a
new theory has been presented to explain
the increased prevalence of atopic
and autoimmune diseases: the lack of
sunshine or vitamin D deficiency - the
sunshine hypothesis. This hypothesis
may contribute to explain the rising
prevalence or the severity of other conditions,
as there are now evidence of vitamin
D receptors in many cells, besides
enterocytes namely the kidney tubular
cells and osteoblasts, and the association
with obesity and asthma.
Description
Keywords
Vitamina D cĆ©lulas Tregs doenƧas atĆ³picas doenƧas auto-imunes obesidade asma Vitamin D Tregs cells atopic diseases autoimunne diseases obesity asthma
Citation
Nascer e Crescer 2008; 17(3): 125-128