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Measurement of Solar Ultraviolet-B in Riyadh: Its Significance in Studies on Vitamin D Deficiency in Saudi Arabia

1984; King Faisal Specialist Hospital and Research Centre; Volume: 4; Issue: 4 Linguagem: Inglês

10.5144/0256-4947.1984.307

0975-4466

Mohammed A. Hannan, Adnan El‐Yazigi, Farouk A.H. Al-Watban, Nizar Feteih,

Vitamin D Research Studies

Original ArticlesMeasurement of Solar Ultraviolet-B in Riyadh: Its Significance in Studies on Vitamin D Deficiency in Saudi Arabia Mohammed A. Hannan, PhD Adnan El-Yazigi, PhD Farouk A. H. Al-Watban, and MSc, PhD Nizar FeteihMD, FCCP, FACC Mohammed A. Hannan Scientist I, Biological Research Department, Research Centre, Riyadh 11211, Saudi Arabia Search for more papers by this author , Adnan El-Yazigi Scientist III, Biological Research Department, Research Centre, Riyadh 11211, Saudi Arabia Search for more papers by this author , Farouk A. H. Al-Watban Deputy Director, Research Centre, Riyadh 11211, Saudi Arabia Search for more papers by this author , and Nizar Feteih Consultant Cardiologist, King Faisal Specialist Hospital and Research Centre, Riyadh 11211, Saudi Arabia Search for more papers by this author Published Online:1 Oct 1984https://doi.org/10.5144/0256-4947.1984.307SectionsPDF ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail AboutABSTRACTABSTRACTA sunburning ultraviolet meter with an automatic recorder was used to measure the incidence of solar ultraviolet-B in Riyadh, Saudi Arabia. The data recorded in arbitrary units at half-hour intervals for a month were pooled and the average daily incidence of this radiation was calculated. The results are also expressed in sun units (SU), each of which is represented by 440 counts in the meter and is approximately equivalent to one minimal erythemal dose of UV-B. The data collected so far appeared to be consistent with the natural expectation of UV-B irradiance on the earth’s surface at the latitude where Riyadh is located. A comparison of data obtained in Riyadh and various locations in the United States showed that the average daily UV-B irradiance in the Riyadh area is on the high side. We conclude that atmospheric dust particles have no significant effect on the average daily UV-B incidence in this area and hence such a factor should not be implicated in vitamin D deficiency in Saudi Arabia.INTRODUCTIONThe synthesis of vitamin D in human skin is dependent upon ultraviolet (UV)-induced photo-conversion of 7-dehydrocholesterol to previtamin D3. Therefore, inadequate exposure to sunlight as well as shielding of UV light by skin pigmentation have been implicated in vitamin D deficiency.1–3 Controversial results obtained with single and repeated exposures to solar UV and their relationship to vitamin D synthesis4,5 warrant further investigation of correlations between intensity of solar UV and vitamin D status in different populations. The occurrence of vitamin D deficiency in Saudi Arabian population has been inferred from studies demonstrating low serum concentrations of 25-hydroxycholecalciferol (25-OHD) in a number of Saudi subjects.6,7 It is believed that both dietary factors and reduced exposure to sunlight could account for vitamin D deficiency in this population. In addition, there is a speculation that a significant shielding of solar UV light by atmospheric dust particles may be one of the factors responsible for vitamin D deficiency in Saudi Arabia.6,7 The absence of any reported data on the actual measurement of the intensity of solar UV radiation in this country poses a limitation in establishing a relationship between the level of sunlight exposure and vitamin D status in the population. Therefore, the present studies were initiated to determine the cumulative irradiance of the biologically most significant part of the solar UV spectrum in the Riyadh area.The spectrum of solar UV light reaching the earth’s surface ranges from 290 to 390 nm. This spectrum is divided into two parts; the wavelengths covering 320 to 390 nm are referred to as UV-A and 290 to 320 nm as UV-B. The UV-B part of the spectrum is the most biologically effective radiation, particularly concerned with sunburning, skin cancer, and synthesis of vitamin D.8 UV-A radiation has some indirect and direct biological effects but these are considered to be much less significant compared to those of UV-B. Furthermore, the short wavelengths of UV-B are subject to much more attenuation by atmospheric factors than UV-A. In view of these factors, the present study was designed to monitor only solar UV-B over a period of time.MATERIALS AND METHODSApparatusA sunburning ultraviolet meter and a detector with an automatic recorder and a data storage system were obtained from Temple University, Philadelphia, Pennsylvania, USA. The meter was designed by Berger9 to specifically measure intensity of the UV-B spectrum (290-320 nm) of sunlight.UV-B MeasurementThe meter records UV-B in arbitrary counts; 440 counts represents one sun unit (SU). An SU is a biologically weighted unit in the sense that it is approximately equivalent to the minimal erythemal dose (MED), which causes an average Caucasian’s skin to show a barely perceptible reddening 4 to 8 hours after exposure to UV-B. The effective energy of one SU is approximately 2 x 103 J/m2 relative to 297 nm.9 Meter readout is located in the laboratory and is connected to a weatherproof sunburning UV detector placed on the rooftop of the King Faisal Specialist Hospital and Research Centre in Riyadh. Accumulated counts are automatically recorded on a magnetic tape as well as a paper tape every half-hour. Daily cumulative data for UV-B irradiance are calculated from the half-hourly records. An average daily rate of incident UV-B radiation is then estimated from the readings for one month. The same type of meters, centrally calibrated at the Temple University, are used in various locations in the United States to monitor the incident solar UV-B radiation. Daily cumulative UV-B data collected for the months of September, October, November, and December in 1974 at several stations in the United States were used for comparison with the UV-B radiation monitored in Riyadh.RESULTSDistribution of UV-B counts recorded at half-hour intervals for 10 consecutive days in the month of September 1983 in Riyadh is shown in Fig. 1. During this period, the average noontime UV-B irradiance in Riyadh was found to be 3.4 SU/hr. These half-hourly counts were integrated for the month and an average daily rate was obtained. For the month of September, it was estimated that the average daily UV-B irradiance in Riyadh reached about 17.9 SU. Berger9 has shown a relationship between SU and minimal erythemal dose as well as the maximum dose of UV-B in SU expected with an overhead sun. According to Berger’s estimate, 3 SU/hr would mean that an average Caucasian would receive a minimal erythemal dose in approximately 20 minutes of exposure to the solar UV-B under study. From the data shown by Berger,9 it would appear that the amount of UV-B in sunlight recorded in Riyadh in the month of September is sufficient to cause significant biological effects. In the summer months, one would expect that larger amounts of UV-B will reach the earth’s surface in this area because of changes in the solar altitude.Fig. 1. Distribution of UV-B counts/0.5 hr. recorded continuously for 10 days in September 1983 in Riyadh.Download FigureAverage daily UV-B counts obtained in Riyadh for the months of September, October, November, and December (in 1983) are presented in Fig. 2 in comparison with those recorded for the same months (in 1974) at 10 locations in the United States. Although these data show a fair correlation between latitudes and incidence of UV-B, there are exceptions (e.g., Philadelphia and Fort Worth) that could be attributed to the atmospheric conditions such as cloud cover which are known to occur in these areas.Fig. 2. A comparison of average daily UV-B counts recorded in Riyadh with those obtained in 10 stations in the United States.Download FigureData presented in Fig. 2 also show a seasonal change in the amounts of solar UV-B as reflected by the counts of different months. For example, the amount of UV-B radiation incident on the earth’s surface begins to decrease as the winter months approach. Because of the effect of the solar altitude and of climatic factors on UV-B counts in different months, it would be more desirable to estimate the annual cumulative UV incidence rate for global comparisons. While such studies are under way, the results presented here show that the UV-B counts recorded for the 4 months in Riyadh, located at 24.4 °N latitude, are much closer to those obtained in Mauna Loa, Hawaii (21.1 °N latitude), and are much higher than those recorded in all other stations located between 31°N and 44.5 °N latitude in the United States. Saudi Arabia lies approximately between 15° and 32 °N latitude. Also, the sky is relatively clear throughout the year except for infrequent sandstorms and cloud covers. Blowing dust and cloudy weather reduced the UV-B counts in our study as expected; however, such occasions were rare, and they did not have significant effect on the cumulative results obtained for periods of months although these are included in the averaged data. Secondly, in order to make a risk assessment, one should consider what is the natural amount of UV-B which could be received on a clear sunny day. The UV-B data obtained in Riyadh appear to be consistent with the effect of latitude and indicate that sufficient UV radiation is present in the sunlight. Although we do not rule out the occasional small effect of natural airborne dust particles on our UV-B counts, we conclude that those effects are insignificant and do not drastically reduce the amount of solar UV-B radiation incident at ground level in this geographical location.Biological effects of natural sunlight observed in Riyadh10 suggest that potential carcinogenic radiations are present in the sunlight, showing both cytotoxic and genotoxic activities. Yet, the reduced incidence of skin cancer and sunburning in this area6,10 may be attributable to other factors such as lack of humidity and nature of skin pigmentation or use of headdresses. Unlike cancer incidence, vitamin D synthesis does not require a very large solar exposure. Although pigmentation is believed to be a barrier for UV penetration to the skin and consequently a factor in vitamin D deficiency, studies4,5 with repeated exposures of pigmented and nonpigmented skin to UV light suggest that the discrepancy may disappear when one considers repeated exposure to sunlight with relatively high intensity of UV light. While vitamin D deficiency may result from a gross reduction in exposure to] solar UV, it is also possible that it may be caused by either a reduced level of vitamin D precursors or impaired metabolism of this vitamin in the body due to genetic differences. Studies are under way in our laboratory to characterize the kinetics of these processes in randomly selected samples of the Saudi population with known degrees of solar exposures, employing a highly specific high performance liquid chromatography method.In view of the high intensity of UV-B recorded in Riyadh and the potential carcinogenicity of this radiation,10 caution should be exercised in encouraging increased exposure to sunlight, particularly in the humid parts of the country and for those with various skin lesions. While further studies continue seeking the factors responsible for vitamin D deficiency in Saudi Arabia, we reemphasize the current need for strict regulatory action to ensure dietary supplementation with vitamin D, particularly in milk as pointed out earlier by Woodhouse and Norton.6ARTICLE REFERENCES:1. Haddad JG, Hahn TJ: "Natural and synthetic sources of circulating 25-hydroxyvitamin D in man" . Nature 244:515–61973. Google Scholar2. Bachrach S, Fisher J, Parks JS: "An outbreak of vitamin D deficiency rickets in a susceptible population" . Pediatrics 64(6):871–71979. Google Scholar3. Dunnigan MG, Paton JP, Haase S, et al.: "Late rickets and osteomalacia in the Pakistani community in Glasgow" . Scott Med J 7:159–611962. Google Scholar4. Clemens TL, Adams JS, Henderson SL, et al.: "Increased skin pigment reduces the capacity of skin to synthesize vitamin D3" . Lancet 1(8263):74–61982. Google Scholar5. Stamp TC: "Factors in human vitamin D nutrition and in the production and cure of classical rickets" . Proc Nutr Soc 34(2): 119–301975. Google Scholar6. Woodhouse NJ, Norton WL: "Low vitamin D levels in Saudi Arabians" . The King Faisal Specialist Hospital Medical Journal 2(3): 127–311982. Google Scholar7. Sedrani SH, Elidrissy AW, El Arabia KM: "Sunlight and vitamin D status in normal Saudi subjects" . Am J Clin Nutr 38(1):129–321983. Google Scholar8. Giese AC: Is sunlight good for you? In: Living With our Sun's Ultraviolet Rays. New York, Plenum Press, 1976. Google Scholar9. Berger DS: "The sunburning ultraviolet meter: design and performance" . Photochem Photobiol 24(6):587–931976. Google Scholar10. Hannan MA, Paul M, Amer MO, et al.: "A study of ultraviolet radiation and genotoxic effects of natural sunlight in relation to skin cancer in Saudi Arabia" . Cancer Res 44:22192–71984. Google Scholar Previous article Next article FiguresReferencesRelatedDetails Volume 4, Issue 4October 1984 Metrics History Published online1 October 1984 KeywordsVitamin D Deficiency—Saudi ArabiaUltraviolet RaysACKNOWLEDGEMENTSThe authors wish to thank Dr J. Zajackowski and L. Holmberg of Scientific Computing Department of the Research Centre for their help in data analysis. Thanks are also due to Mr B. Fish of the Research Centre and Dr John Godwin, Chairman of Department of Pathology and Laboratory Medicine at the King Faisal Specialist Hospital and Research Centre, for valuable suggestions during the preparation of this manuscript.InformationCopyright © 1984, Annals of Saudi MedicinePDF download