SQU Med J, May 2011, Vol. 11, Iss. 2, pp. 196-200, Epub. 15th May 11
Invited Article
Submitted 2nd Apr 11
Revision ReQ. 20th Apr 11, Revision recd. 23rd Apr 11
Accepted 24th Apr 11

Only a small amount of vitamin D comes from dietary sources, e.g. fish and meat,1 while most of it is known to 
be made by the body as a natural by-product of the 
skin's exposure to sunlight.2 In the early 1900s, the 
discovery of the link between rickets and vitamin 
D deficiency helped to ensure that exposure to the 
ultraviolet B (UVB) fraction of sunlight became 
popular as a preventative medical intervention.3

UVB rays enter the epidermis and release energy 
that changes a pre-existing cholesterol metabolite 
to previtamin D3, which is then slowly converted 
nonenzymatically to vitamin D3 (cholecalciferol). 
Vitamin D3, bound to a specific vitamin D- 

binding protein (DBP), is then transported to the 
liver, where it is enzymatically hydroxylated to 
25-hydroxyvitamin D (calcifidiol or 25(OH)D). 
Although 25(OH)D is only weakly biologically 
active, its circulating level furnishes a good index of 
the bioavailability of vitamin D because it has a long 
serum half-life (2 weeks).4 Then, 25(OH)D, bound 
to DBP, is transported to the kidney and other 
organs, where it is hydroxylated at the 1 position to 
produce 1,25(OH)2D, the most biologically active 
form of vitamin D.4

From our point of view, sun education started 
to emphasise the importance of protection from 
harmful ultraviolet rays (UVR), especially after 

Office of H.E. the Undersecretary of Planning, Ministry of Health, Muscat, Oman.
*Corresponding Author email: drmoness@gmail.com

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
 25:مفتاح الكلمات

aBstract: Only small amounts of vitamin D come from dietary sources as it is mainly synthesised in the skin 
from the ultraviolet B (UVB) fraction of sunlight if the person is sufficiently exposed to direct sunlight. Vitamin 
D deficiency has been well documented in Oman. The "2004 Oman National Micronutrients Survey" and other 
recent studies revealed that vitamin D3 stores are low among healthy Omani females of childbearing age and 
pregnant women. This situation is confusing as Oman is known to be one of the sunniest countries in the world.  
However, it is known that most Omani women are well covered and for various reasons avoid sun exposure. The 
article addresses a question about the balance that should be maintained between excessive sun exposure that 
leads to an increased risk of skin cancer, and healthy exposure that provides sufficient ultraviolet radiation (UVR) 
to maintain adequate vitamin D levels. In order to avoid vitamin D deficiency, sun exposure or protection messages 
must be tailored according to different situations, in recognition of the complex combination of personal, cultural 
and social factors that affect vitamin D synthesis in the skin.

Keywords: Vitamin D deficiency, 25-hydroxyvitamin D, Sunlight, Ultraviolet Rays, Skin Cancer, Oman

SOUNDING BOARD

To Be or Not To Be Exposed to Direct Sunlight
Vitamin D Deficiency in Oman

Moeness M. Alshishtawy



Moeness M. Alshishtawy

Sounding Board | 197

the strong involvement of the United Nations 
(UN) in work to understand the health effects of 
UVR exposure. This was established at the UN 
Conference on Environment and Development in 
1992. The trigger for that was the recognition that 
the ozone layer was being depleted and that the 
risk of diseases resulting from excessive exposure 
to UVR, particularly skin cancers, would probably 
increase.5 

Several studies have demonstrated that exposure 
to environmental levels of UVR alters the activity 
and distribution of some of the cells responsible 
for triggering immune responses in humans. 
Consequently, sun exposure may enhance the risk 
of infection with viral, bacterial, parasitic or fungal 
infections, which has been demonstrated in a variety 
of animal models.6 The known health effects of UVR 
include also photokeratitis and photoconjunctivitis. 
Moreover, sun exposure, in particular exposure to 
UVB, appears to be a major risk factor for cataract 
development.7 Regarding skin, exposure to UVR is 
considered to be a major aetiological factor for its 
three common forms: basal cell carcinoma (BCC), 
squamous cell carcinoma (SCC) and malignant 
melanoma (MM). Non-melanoma skin cancers, 
BCC and SCC, are most frequent on parts of the 
body that are commonly exposed to the sun such as 
ears, face, neck and forearms. This implies that long-
term, repeated UVR exposure is a major causative 
factor. Moreover, there is a clear relationship, in 
some countries, between an increasing incidence 
of non-melanoma skin cancers and decreasing 
latitude, i.e. higher UVR levels.6 On the other hand, 
the causes of malignant melanoma (MM) are not 
fully understood. However, several epidemiological 
studies support a positive association with a history 
of sunburn, particularly sunburn at an early age. 
Tumour development may be linked to high, 
intermittent exposure to solar UVR,6 such as at 
weekends or on holiday.7 The higher incidence of 
malignant melanoma in indoor workers compared 
to outdoor workers supports that notion.7 Studies 
show also that malignant melanoma risk is higher 
in people with a history of non-melanoma skin 
cancers and of solar keratoses, both of which are 
indicators of cumulative UV exposure.6

In assessing how much sun exposure is needed 
for adequate vitamin D production, one should be 
aware that there is a threshold level of UVB required 
to induce vitamin D production.8 However, the 

exact dose of UVR exposure for optimal vitamin 
D levels is not known, particularly as the required 
UVR dose will be influenced by host factors. Whole 
body exposure in a bathing suit to one minimum 
erythemal dose (MED) of UVR is equivalent to 
ingesting 10,000 international units of vitamin 
D.9 MED is defined as the UVR exposure that will 
produce a just perceptible erythema 8–24 hours 
after irradiation of the skin. The MED is specific 
to each individual and varies with the source of 
UVR, the tanning capacity and any adaptation from 
previous exposures.10

A low level of casual sun exposure, even during 
summer, will result in only very small amounts of 
endogenous vitamin D3 production.11 The effects of 
sunlight exposure on vitamin D3 synthesis are also 
decreased by the use of sunscreens and in individuals 
with darker skin pigmentation12 because of the 
presence of high concentrations of melanin in the 
stratum corneum that severely inhibits vitamin D3 
production.10 In addition to that, concentrations of 
25(OH)D in blood serum—the best clinical index of 
vitamin D status—decline with age due to declining 
intake, decreased sun exposure and, perhaps most 
importantly, less efficient skin synthesis of vitamin 
D3.13 Thus, for a person with moderately fair skin, 
exposure of face, hands and arms for 6–7 minutes at 
10:00 or 14:00 in summer (or 9–12 minutes in winter) 
in northern Australia (latitude 17° south), should 
produce around 1,000 IU of vitamin D, an amount 
sufficient to maintain vitamin D concentrations in 
the normal range. The equivalent exposure required 
at a higher latitude such as Tasmania (41–43° south) 
is 7–9 minutes in summer, but 40–47 minutes in 
winter.14 However, some argument remains over 
the range of concentrations of vitamin D in blood 
that should be considered ‘normal’. Currently, 50 
nmol/L is accepted as the lower limit of sufficiency,5 
although a study from Finland, suggested 80 nmol/L 
as the minimum level in blood able to prevent 
physiological changes associated with vitamin D 
insufficiency.15

Although a low prevalence should be expected, 
studies carried out in the last two decades show a 
high prevalence of vitamin D deficiency in many 
tropical countries,16 including Oman. In 2004, the 
Ministry of Health (MOH), Oman, in collaboration 
with the Centers for Disease Control and Prevention 
(CDC), the World Health Organization (WHO) 
and the United Nations International Children's 



To Be or Not To Be Exposed to Direct Sunlight 
Vitamin D Deficiency in Oman

198 | SQU Medical Journal, May 2011, Volume 11, Issue 2

Emergency Fund (UNICEF) conducted a cross-
sectional household-based survey of micronutrient 
status using the sophisticated technique of high-
performance liquid chromatography (HPLC) in 
the MOH Central Public Health Laboratory to 
analyse vitamin D and other micronutrients in 
serum samples from 832 households. The survey 
clusters were selected using the PPS (proportional 
to population size) sampling methodology.17 A sub-
sample of 298 non-pregnant women of child bearing 
age was analysed for serum 25(OH)D. Alarmingly 
21.4% of the women included in the survey were 
found to be vitamin D deficient (<27.0 nmol/L).17 

Almost half of the women (47%) tested had serum 
25(OH)D levels below 37.5 nmol/L, while only 10% 
of the women had levels above 75 nmol/L.18

A more recent study by Al-Kindi in 201016 
investigated serum 25(OH)D levels among 41 
apparently healthy Omani women of childbearing 
age. All the women had a 25(OH)D level <50 
nmol/L as the cut-off for deficiency. Another study 
conducted by Al Kalbani et al. in 201019 investigated 
the vitamin D status of pregnant Omanis by 
measuring their circulating 25(OH)D levels. In that 
study, blood samples were obtained from a cohort 
of 103 consecutive healthy pregnant Omanis on 
their first antenatal visit to the hospital. The study 
revealed that vitamin D deficiency ([25(OH)D] 
<25 nmol/L) was present in 34 cases (33%), ‘at risk’ 
levels ([25(OH)D] = 25–50 nmol/L) were found in 
67 cases (65%); two cases (1.9%) had values between 
50 and 75 nmol/L, and not one case was found in the 
optimal range (25(OH)D >75 nmol/L). The results 
confirmed that vitamin D3 stores are low in Omani 
females of reproductive age. The findings of the 
study were found by Al Kalbani and her colleagues 
to be similar to those reported earlier in Saudi 
Arabia and recently in the UAE and Qatar.20,21,22

These recent studies conducted in Oman give a 
warning that subclinical vitamin D deficiency may 
be prevalent amongst Omani women and indicate 
the need for vitamin D replacement especially 
during pregnancy and lactation.16,19 This situation 
is surprising as Oman is known to be one of the 
sunniest countries in the world and its people are 
thus expected to have adequate sun exposure. This 
unexpected situation may be attributed to social 
and cultural factors16 as the conservative dress 
of Omani women, especially those who wear the 
veil, blocks exposure to sunlight. Added to that, 

the reduction in outdoor leisure time that has 
accompanied urbanisation in Oman and the rise 
in office-based work has lead to an increased lack 
of sunlight exposure. Females, particularly those 
who are sensitive to the sun's UV rays, are more 
concerned about their appearance and health. They 
are unwilling to get dark-coloured skin or sunburn, 
and so avoid being exposed directly or indirectly to 
sunlight.

So, the boundaries between the risks and the 
benefits of UVR are unclear and the question 
therefore arises: “What is the balance between 
healthy sun exposure that provides sufficient UVR to 
maintain adequate vitamin D levels in blood serum, 
and excessive exposure that leads to an increased 
risk of skin cancer?” Unfortunately, public health 
campaigns aiming to decrease the incidence of skin 
cancer urged people to limit exposure to ultraviolet 
light, which is important for maintenance of vitamin 
D levels, especially in at-risk groups such as those 
who are elderly, who suffer from malabsorption or 
who have dark skin (particularly if they wear a veil).23 
It is important also to mention that the guidelines 
for decreasing exposure included directives from 
the American Academy of Pediatrics (AAP) that 
infants younger than 6 months should be kept out 
of direct sunlight, children’s activities that minimise 
sunlight exposure should be selected, and protective 
clothing as well as sunscreens should be used.24 
Accordingly, one consequence of avoiding possibly 
harmful sun exposure could be a reduced amount 
of physical activity, especially when school, work 
and rec-reational activities are usually scheduled 
outdoors between 10:00 and 16:00. Sun protection 
messages may, thus, inadvertently increase health 
risks related to physical inactivity such as obesity 
and cardiovascular disease.23

All these irritatingly contradictory relationships 
make it very difficult to determine what the adequate 
sunshine exposure time is for any given person. The 
message to protect against excessive UVR exposure 
was seen to be correct in countries with abundant 
sunshine and populated by fair-skinned inhabitants. 
Even for populations that remain in the physical 
environments for which they are evolutionarily 
suited, marked changes in the social environment 
now predispose people to diseases associated with 
under- or over-exposure to UVR. Similarly, in 
populations that have moved from their traditional 
habitats, problems of both excess sun exposure and 



Moeness M. Alshishtawy

Sounding Board | 199

vitamin D insufficiency are clearly evident.5 
The first national cancer council to recognise the 

importance of balance in recommendations about 
sun exposure was the Cancer Council Australia 
in its 2005 position statement "Risks and benefits 
of sun exposure".23 The statement did provide 
sufficient guidance on optimum levels of exposure.5 
However, the correct answers to several questions 
are still under debate: “What is the optimal level of 
vitamin D?”, “What is the amount of UVR needed to 
maintain an adequate vitamin D level?”, and “What 
is the optimal age-appropriate UVR dose?” 

The conclusion is that increased UVR exposure 
is known to have harmful health consequences; 
however, UVR exposure also has some beneficial 
effects, especially in relation to vitamin D production. 
Therefore, a ‘one message fits all’ approach is not 
appropriate. Sun exposure or protection messages 
may need to be shaped to different situations, in 
recognition of the complex combination of host 
factors, e.g. age, sex, race, skin pigmentation, and 
sun-seeking or sun-avoidance practices. This matrix 
of considerations becomes even more complex 
when a diversity of cultural and social environments 
are taken into account. Added to that, the lack of 
clear guidelines may lead to inappropriate personal 
solar exposure. The substantial challenge for health 
workers is to translate their knowledge into readily 
comprehensible public health messages and, 
subsequently, to take account of the accretion of 
upcoming evidence-based information.

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