Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 112

A small degree of UV exposure is needed by humans to support the synthesis of vit-
amin D. This vitamin is important for the growth, development and maintenance of bone.
Vitamin D deficiency increases the risk of osteoporosis, bone fractures and the condition
known as rickets in children. Low levels of vitamin D are also thought to increase the risk
of several internal cancers, some autoimmune diseases and cardiovascular diseases, includ-
ing hypertension. People with dark skin need more UV exposure than fair-skinned people
to synthesize the same amount of vitamin D. As we age, the efficiency of this process de-
clines. It is not yet clear whether oral vitamin D supplementation provides similar benefits.
Erythemal UV exposure is a term used to measure UV irradiance (the amount of en-
ergy arriving at a surface) that takes into account the potential of UV-A and UV-B to cause
biological damage. However, it has been very difficult to demonstrate a direct correlation
between the amount of exposure to UV-B radiation and a particular biological effect. Fact-
ors contributing to this difficulty include varying degrees of susceptibility amongst differ-
ent species and even between populations from the same species sampled from different
geographical regions. They also include interactions with other stressors, such as nutrition-
al status, or the presence of biologically active chemicals. For example, in humans, a wide
range of substances, including birth control pills, cyclamates, tetracycline antibiotics and
coal tar distillates used in some antidandruff shampoos and some cosmetics, can exacer-
bate the photochemical effects of UV-B radiation. Similarly, aquatic organisms in areas of
crude oil and heavy metal pollution (including cadmium, selenium and copper) are more
sensitive to the effects of UV-B.
UNEP produces periodic ozone assessments that focus on the human and envir-
onmental effects of ozone depletion. These reports are therefore complementary to the
physical/chemical assessments produced by the International Meteorological Organization
(IMO). According to the 2010 UNEP assessment, peak values of erythemal UV radiation
in mid-northern latitudes may have tripled by2065if it were not forthe actions taken under
the Montreal Protocol. Levels of this magnitude would have carried the risk of substantial
human health and environmental impacts, which hopefully we will not now experience.
As we have seen, implementation of the Montreal Protocol has stabilized the accumulation