SORU: aşağıdaki parçaya göre cevaplayınız
According to the passage, the synthesis of vitamin D in the body ----.
Dark-skinned people require longer sunlight
exposure than light-skinned people: heavily
pigmented skin arrives at the same plateau of
vitamin D synthesis in three hours as fair skin
in 30 minutes. The ultraviolet (UV) rays of the
sun that promote vitamin D synthesis are
blocked by heavy clouds, smoke or smog.
Differences in skin pigmentation and smog
may account for the finding that dark-skinned
people in northern, smoggy cities are more
prone to rickets. For these people, and for
those who are unable to go outdoors
frequently, dietary vitamin D is most important.
Deficiency is especially likely in older adults
because they typically drink little or no milk,
their exposure to sunlight is limited, and the
skin, liver and kidneys lose their ability to make
and activate vitamin D with advancing age.
Depending on the UV radiation used, the UV
rays from tanning lamps and tanning booths
may also stimulate vitamin D synthesis but the
hazards outweigh any possible benefits. If the
lamps are not properly filtered, people using
tanning booths risk burns, damage to the eyes
and blood vessels, and skin cancer.