Estimating personal solar ultraviolet radiation exposure through time spent outdoors, ambient levels and modelling approaches

BACKGROUND

 Evidence on validation of surrogates applied to evaluate the personal exposure levels of solar ultraviolet radiation (UVR) in epidemiological studies is scarce.

OBJECTIVES

 To determine and compare the validity of three approaches, including (i) ambient UVR levels, (ii) time spent outdoors, and (iii) a modelling approach integrating the aforementioned parameters, to estimate personal UVR exposure over a period of six months among indoor and outdoor workers and in different seasons (summer/winter).

METHODS

 This validation study was part of the EU ICEPURE project and was performed between July 2010 and January 2011 in a convenience sample of indoor and outdoor workers in Catalunya - Spain. We developed linear regression models to quantify the variation in the objectively measured personal UVR exposure that could be explained, separately, by the ambient UVR, time spent outdoors, and modelled UVR levels.

RESULTS

Our 39 participants - mostly male and with a median age of 35 years- presented a median daily objectively measured UVR of 0.37 standard erythemal doses (SEDs). The UVR dose was statistically significantly higher in summer and for outdoor workers. The modelled personal UVR exposure and self-reported time spent outdoors could reasonably predict the variation in the objectively measured personal UVR levels (R² = (0.75, 0.79)), whereas ambient UVR was a poor predictor (R² =0.21). No notable differences were found between seasons or occupation.

CONCLUSIONS

 Time outdoors and our modelling approach were reliable predictors and of value to be applied in epidemiological studies of the health effects of current exposure to UVR.

UVR exposure and vitamin D in a rural population. A study of outdoor working farmers, their spouses and children

BACKGROUND

Living and working in the countryside may result in excessive UVR exposure, with increased risk of skin cancer. Some sun exposure is, however, recommended, since vitamin D production is UVB-dependent.

OBJECTIVES

To examine UVR exposure and vitamin D levels in a rural population of outdoor working male farmers, their indoor working spouses and their children, expected to receive high UVR exposure.

METHODS

Prospective, cohort study. During the summer 2009 daily, personal UVR exposure and sun behaviour were recorded by dosimetry and diaries (17 403 days). Vitamin D was measured at the end of summer and the following winter.

RESULTS

Risk behaviour (= exposure of shoulders/upper body to the sun), beach days, sunscreen use and sunburns were infrequent. Farmers and boys had the highest daily UVR exposure (both 1.5 SED per day), likewise on work days. On non-work days the UVR exposure was even higher (up to 2.0 SED per day). Farmers, girls and boys had a higher chronic UVR exposure than the spouses, who had more intermittent high UVR exposure. Vitamin D levels did not differ between family members. At the end of summer 16% of the participants were vitamin D insufficient, the following winter, 61%. Some UVR exposure variables correlated positively, but weakly, with vitamin D levels.

CONCLUSIONS

UVR exposure was generally high among this study population, however, vitamin D levels still dropped below the recommended level during winter for most participants. Differences in UVR exposure between the groups did not result in differences in vitamin D levels.

Determinants of personal ultraviolet-radiation exposure doses on a sun holiday

BACKGROUND

A great number of journeys to sunny destinations are sold to the Danish population every year. We suspect that this travel considerably increases personal annual ultraviolet-radiation (UVR) exposure doses. This is important because such exposure is the main cause of skin cancer, and studies have shown a correlation between intermittent solar UVR exposure and malignant melanoma.

OBJECTIVES

To prospectively monitor the behaviour of a group of sun seekers during a winter sun holiday and to study the impact of behaviour on personal UVR exposure doses.

METHODS

In this observational study 25 Danish sun seekers were closely monitored by on-site investigators for 6 days during a winter sun holiday in the Canary Islands, thus avoiding the possible recall bias of retrospective studies with questionnaires. The volunteers recorded their location, clothing and sunscreen use in diaries, and their UVR doses were measured by personal UVR dosimeters worn on the wrist. This resulted in 3450 half-hour registrations during 150 participation days.

RESULTS

On average, each volunteer received a total UVR dose of 57 standard erythema doses over 6 days, which is 43% of the annual UVR dose of a Danish indoor worker. Their exposed body area, sunscreen use and percentage of body with sunscreen application were positively correlated with their personal UVR doses, and there was also a strong relationship between location and UVR doses received.

CONCLUSIONS

The behaviour of the volunteers had a major impact on their personal UVR doses. Our results emphasize the importance of changing the behaviour of sun seekers with protanning attitudes to reduce their personal annual UVR exposure doses, and possibly their risk of skin cancer.

Validation of self-reported erythema: comparison of self-reports, researcher assessment and objective measurements in sun worshippers and skiers

BACKGROUND

Most epidemiological data of sunburn related to skin cancer have come from self-reporting in diaries and questionnaires. We thought it important to validate the reliability of such data.

OBJECTIVE

To validate the quality of self-reported erythema by sun worshippers and skiers, and to validate the ability to determine erythema visually compared with objectively measured erythema.

METHODS

The skin in a group of sun worshippers in Tenerife and of skiers in Austria was closely monitored over a week. The participants used a diary to record any erythema assessed on different skin sites and underwent a twice daily skin examination by researchers who assessed erythema on the same sites. Lastly, the erythema assessment was validated by objective measurements.

RESULTS

We found that the participants' agreed with researchers' assessment of erythema in only 57-61% of cases, and that the researchers detected up to 28% more of the objectively measured erythema than the participants did. We also found that, even for the trained eye (researchers), it was difficult to detect an increase in erythema as only 71-91% of those cases with an increase >15 in measured erythema percentage were detected in the evening. Possibly, detection was impeded by a simultaneous increase in pigmentation.

CONCLUSION

Self-assessment of erythema from diaries is unreliable. Erythema is considerably underestimated and possibly neglected. Even for the trained eye, it can be difficult to detect erythema.

Interdependence between body surface area and ultraviolet B dose in vitamin D production: a randomized controlled trial

BACKGROUND

Ultraviolet (UV) B radiation increases serum vitamin D level expressed as 25-hydroxyvitamin-D(3) [25(OH)D], but the relationship to body surface area and UVB dose needs investigation.

OBJECTIVE

To investigate the importance of body surface area and UVB dose on vitamin D production after UVB exposure.

METHODS

We randomized 92 participants to have 6%, 12% or 24% of their skin exposed to 0·75 (7·5 mJ cm(-2) at 298 nm using the CIE erythema action spectrum), 1·5 (15 mJ cm(-2) ) or 3·0 (30 mJ cm(-2) ) standard erythema doses (SED) of UVB. Each participant underwent four UVB exposures at intervals of 2-3 days. Skin pigmentation and 25(OH)D levels were measured before and 48 h after the final exposure.

RESULTS

The increase in 25(OH)D after irradiation [Δ25(OH)D] was positively correlated with body surface area (P = 0·006; R(2) = 0·08) and UVB dose (P < 0·0001; R(2) = 0·28), and negatively correlated with baseline 25(OH)D (P < 0·0001; R(2) = 0·18), for the entire data sample. However, when analysing each body surface area separately, we found a significant UVB response correlation for 6% (P < 0·0001; R(2) = 0·48) and 12% (P = 0·0004; R(2) = 0·35), but not for 24%. We also found a significant skin area response correlation for 0·75 SED (P < 0·0001; R(2) = 0·56), but not for 1·5 and 3·0 SED when analysing each UVB dose separately. The relationships did not change significantly after adjustment of Δ25(OH)D for baseline 25(OH)D.

CONCLUSION

The increase in 25(OH)D depends mainly on the UVB dose; however, for small UVB doses the area of irradiated body surface is important.

Ultraviolet radiation exposure pattern in winter compared with summer based on time-stamped personal dosimeter readings

BACKGROUND

Personal annual ultraviolet (UV) radiation data based on daily records are needed to develop protective strategies.

OBJECTIVES

To compare UV radiation exposure patterns in the winter half-year (October-March) and the summer half-year (April-September) for Danish indoor workers.

METHODS

Nineteen indoor workers (age range 17-56 years) wore personal UV dosimeters, measuring time-stamped UV doses continuously during a year. The corresponding sun exposure behaviour was recorded in diaries. Similar data were collected for 28 volunteers during sun holidays in the winter half-year. The relationship between UV dose and sun exposure behaviour was analysed.

RESULTS

The ambient UV dose during the winter in Denmark (at 56 degrees N) was 394 standard erythema doses (SED) or 10.5% of the annual ambient UV dose. In winter compared with summer the subjects had: (i) a lower percentage of ambient UV radiation, 0.82% vs. 3.4%; (ii) a lower solar UV dose in Denmark, 3.1 SED (range 0.2-52) vs. 133 SED (range 69-363); (iii) less time outdoors per day with positive dosimeter measurements, 10 min vs. 2 h; and (iv) no exposure (0 SED) per day on 77% vs. 19% of the days. Sun holidays outside Denmark in winter gave a median 4.3 SED per day (range 0.6-7.6) and 26 SED (range 3-71) per trip.

CONCLUSIONS

In the winter half-year indoor workers received a negligible UV dose from solar exposure in Denmark and needed no UV precautions. No UV precautions are needed from November to February during holidays to latitudes above 45 degrees N, while precautions are needed the whole year around at lower latitudes.

Ultraviolet exposure patterns of Irish and Danish gardeners during work and leisure

BACKGROUND

Skin cancer, caused by solar ultraviolet (UV) radiation, is a growing problem in Europe. Reliable data on occupational exposure of outdoor workers are needed to develop protective strategies.

OBJECTIVES

To compare UV radiation exposure patterns between outdoor workers in two European populations.

METHODS

Fifty-three gardeners, 31 Irish and 22 Danish (age range 24-69 years) wore personal UV dosimeters, measuring time-stamped UV doses continuously during a 4-month summer period. The current and historical sun exposure pattern was recorded by means of a diary and questionnaire. Assessment of pigmentation, naevi, freckles and solar lentigines was performed. The relationship between UV dose and sun exposure pattern was analysed.

RESULTS

Regarding work days, the Irish had a significantly lower percentage of ambient UV exposure than the Danes, 4.5% vs. 8.1%; a lower UV dose per day, 0.97 standard erythema dose (SED) vs. 1.6 SED; a lower UV dose between 12.00 and 15.00 h, 0.43 SED vs. 0.75 SED; and fewer hours with positive dosimeter measurements, 3.2 h vs. 4.8 h (all values are medians, P < 0.01). Regarding days off work, the same patterns emerged for both UV doses and exposure hours. The Irish had significantly fewer days off than the Danes, median 21 days vs. 49 days, and fewer days with risk behaviour (sunbathing/exposing upper body), median 0 days vs. 8 days (P < 0.01).

CONCLUSIONS

The lower UV exposure received by the Irish gardeners may have been due to indoor breaks during peak ambient UV. Other contributing factors may include differences in natural shade between the parks. Our data suggest that consideration of such factors in scheduling of outdoor work can significantly reduce the occupational UV exposure.

Skin autofluorescence as a biological UVR dosimeter

BACKGROUND/PURPOSE

Collagen is one of the major endogenous skin fluorophores. Alteration in the structure of collagen due to chronic ultraviolet radiation (UVR) exposure may influence the intensity of the autofluorescence. The aim of this study was to investigate the relation between collagen-linked autofluorescence and sun exposure to clarify whether the skin can be used as a biological UVR dosimeter.

METHODS

We conducted an in vivo study with 131 healthy volunteers. Fluorescence was measured from sun-exposed (dorsal forearm, forehead and shoulder) and sun-protected (buttock) skin and corrected for the impact of pigmentation and redness. The excitation wavelengths (Ex) and emission wavelengths (Em) were: Ex330:Em370, Ex330:Em455 and Ex370:Em455 nm. Individual UVR exposure data were collected both retrospectively and prospectively using questionnaires and electronic personal UVR dosimeters for a summer period.

RESULTS

Age, but not sex, skin type or smoking habits correlated significantly positively with skin autofluorescence at Ex370:Em455 at all body sites (P<0.001, r(2)=0.08-0.26), and at Ex330:Em455 only at the buttock (P=0.001, r(2)=0.08), whereas age was not correlated with Ex330:Em370. Sun-protected buttock skin had significantly higher autofluorescence than sun-exposed skin (P-values<0.0001). Because of great between-subject differences in autofluorescence at different body sites, and because the autofluorescence at the unexposed buttock represents the baseline value, individual correction of skin autofluorescence measurement with that of the buttock was performed. Different measures of individual chronic cumulative UVR doses correlated significantly negatively with the skin autofluorescence ratio (F(ratio)), but the correlations were poor (r(2)=0.03-0.10).

CONCLUSION

The results indicate that the collagen-linked skin F(ratio) might be best to use as a measure of individual photodamage, a UVR dose effect, and that it is also a better marker of individual cumulative UVR dose than the used UVR exposure measurements. The methods used to obtain UVR exposure data might not be sensitive and specific enough.

Solar UVR exposures of indoor workers in a Working and a Holiday Period assessed by personal dosimeters and sun exposure diaries

BACKGROUND/AIM

The aim of this study was to quantify ultraviolet radiation (UVR) exposure of fully employed indoor workers during a Working Period and a Holiday Period in the summer months. A further aim was to investigate the correlation between individual personal UVR dosimeter reading and self-reported data in a diary about sun exposure habits and to investigate whether skin type, age and gender influence sun exposure.

METHODS

The solar UVR, in standard erythema doses (SED) measured by UV sensitive spore-film filter type personal dosimeters (VioSpor), and sun exposure diaries were compared. The study included 44 healthy Danish adult indoor workers during a Working Period of a mean of 13 days and a Holiday Period of a mean of 17 days from June to September.

RESULTS

The individual total UVR exposure correlated significantly (P<0.001) in both the Holiday and Working Periods with individual total hours spent outdoors from 07:00 to 19:00 and with skin area exposure hours. There was no significant correlation between sun exposure dose and gender, age or skin type I-IV, or between the individual solar exposure dose in the Working and the Holiday Period. However, subjects with UVR exposures in the upper quartile spent their Holiday Period in Southern Europe, and/or had been more than the mean time outdoors at the beach/sea and/or between 12:00 and 15:00. Subjects with UVR exposure in the lower quartiles spent their holidays in Denmark or Northern Europe and did not stay at the beach at all. They received an average solar UVR dose which was 22% of ambient in Denmark in the same period while subjects having their holidays in Southern Europe received as much as 90% of the ambient dose in Denmark.

CONCLUSIONS

Despite information campaigns to avoid the midday sun, on average 35% of the recorded hours outdoors were spent between 12:00 and 15:00 in the Holiday Period. Total hours outdoors give the best estimate of the total sun exposure dose. Registration in a diary of total hours outdoors and whether the Holiday Period was in Northern or Southern Europe can be used to predict the solar exposure dose in a Holiday Period of a few weeks.

The wrist is a reliable body site for personal dosimetry of ultraviolet radiation

The purpose of this study was to investigate the reliability of measuring solar ultraviolet radiation (UVR) doses with personal UV dosimeters worn on the wrist. Individual solar UVR exposure was measured over one day under standardised conditions (One-day Beach Study), and over an extended period of time with varying UV exposure and activities (Holiday Study). Dosimeters of a UV-sensitive spore-film filter type (VioSpor) were placed on the right wrist and on the top of head of the test subjects. The wrist was chosen as being a practical position for personal dosimetry and the head position as an internal control for maximal personal UV doses. The One-day Beach Study took place in the vicinity of Copenhagen in June 1998 over 5 h and included 11 subjects. The Holiday Study included 9 subjects during a period with a mean of 14 days in Scandinavia and Europe from June to September 1998. The head position received the highest UV dose in all subjects in both studies. In both studies, despite considerable individual variation, the mean wrist dose was the same (50%) of that received on the head, although the wrist dose correlated significantly with head dose (P<0.01) only in the Holiday Study. We conclude that the wrist position is a practical and convenient body site for personal dosimetry, yielding reliable results in group exposure studies.