Solar forcing of drought frequency in the Maya lowlands.
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We analyzed lake-sediment cores from the Yucatan Peninsula, Mexico, to reconstruct the climate history of the region over the past 2600 years. Time series analysis of sediment proxies, which are sensitive to the changing ratio of evaporation to precipitation (oxygen isotopes and gypsum precipitation), reveal a recurrent pattern of drought with a dominant periodicity of 208 years. This cycle is similar to the documented 206-year period in records of cosmogenic nuclide production (carbon-14 and beryllium-10) that is thought to reflect variations in solar activity. We conclude that a significant component of century-scale variability in Yucatan droughts is explained by solar forcing. Furthermore, some of the maxima in the 208-year drought cycle correspond with discontinuities in Maya cultural evolution, suggesting that the Maya were affected by these bicentennial oscillations in precipitation. (+info)
Stability of attenuated live virus rabies vaccine in baits targeted to wild foxes under operational conditions.
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The viability of an attenuated live virus rabies vaccine in a bait targeted to red foxes was examined under various operational conditions in a series of experiments in Ontario. The virus was relatively stable over a 28-day period in the field, losing a mean 0.5, s = 0.2 log10 of virus titer. The micro-environment into which the bait was placed (open cultivated field, grassy meadow, wooded grove, sun or shade) did not make an appreciable difference in the viability of the virus. There was no significant difference (P < or = 0.05) between mean ambient temperatures and the temperature of fluids in blister packs of baits placed in sun or shade. Sixty-three percent of foxes fed baits exposed to sun and shade conditions for 21 days (titer 10(6.2) tissue culture infective doses per 1 mL) developed rabies virus-neutralizing antibodies. Storage of vaccine baits at -30 degrees C prior to bait distribution was important in maintaining virus viability. (+info)
Symptomatic rickets in adolescence.
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AIM: To describe 21 cases of symptomatic rickets in adolescents. METHODS: The setting was a primary and secondary care hospital in Saudi Arabia providing medical care to Saudi Arab company employees and their families. Cases of symptomatic rickets diagnosed between January 1996 and December 1997 in adolescents aged 10 to 15 years were assessed with respect to clinical presentation, biochemical and radiological evaluation, dietary assessment, and estimation of sun exposure. RESULTS: Symptomatic rickets developed in 21 adolescents (20 females), with a prevalence rate of 68 per 100 000 children years. Presentation included carpopedal spasms (n = 12), diffuse limb pains (n = 6), lower limbs deformities (n = 2), and generalised weakness (n = 1). Biochemical findings included hypocalcaemia (n = 19), hypophosphoraemia (n = 9), raised serum alkaline phosphatase (n = 21) and parathormone (n = 7), and reduced 25-hydroxyvitamin D concentrations (n = 7). Radiological studies were suggestive of rickets in only eight children. All children had an inadequate dietary calcium and vitamin D intake. All but one had less than 60 minutes sun exposure per day. CONCLUSION: Even in sunny climates, adolescents, especially females, can be at risk of rickets. Hypocalcaemic tetany and limb pains were the most common presenting symptoms. Radiological evidence was not present in every case. (+info)
Recall bias in self-reported melanoma risk factors.
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The evidence implicating sun exposure in the etiology of melanoma derives largely from case-control studies in which the retrospective assessment of sun exposure suggests potential for significant recall bias. Previous attempts at characterizing and quantifying that bias have had significant methodological limitations. In the International Twin Study, a case-control study of melanoma risk factors in twins conducted from 1980 to 1991, the authors asked melanoma cases and their co-twins to quantify their own exposures and asked which twin had the greater exposure. Recall bias was investigated by assuming that, if bias had occurred, the odds ratio based on the case's response would differ significantly from the odds ratio based on the co-twin's response. Case-derived odds ratios were higher than the odds ratios for the controls for sunbathing in childhood and adulthood and for mole frequency and freckling in childhood, suggesting some recall bias. The odds ratios for ease of burning and tanning appeared unbiased. The belief that sunlight was a cause of melanoma appeared related to an increased odds ratio for sunbathing as a child. There is a continuing need to carefully assess recall bias in the study of melanoma risk factors. (+info)
Topographic variations in normal skin, as viewed by in vivo reflectance confocal microscopy.
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Near-infrared confocal microscopy is a new tool that provides skin images in vivo, with high resolution and contrast at a specific depth. Regional variations in live human skin viewed by confocal microscope have not been studied so far. In vivo reflectance confocal microscopy was performed in 10 adults (eight males, two females) of various skin phototypes. Six topographic sites were studied in each subject: forehead, cheek, inner and outer forearm surfaces, lower back and leg. Epidermal thickness at suprapapillary epidermal plates and rete pegs was measured during real-time imaging and the number and diameter of epidermal keratinocytes in each epidermal cell layer as well as the characteristics of dermal papillae were defined from the grabbed images. Stratum corneum appeared brighter in sun-exposed than in sun-protected areas and particularly pronounced in heavily pigmented individuals. The epidermal thickness at rete pegs, but not the suprapapillary epidermal plate, was greater in sun-exposed areas than in sun-protected sites except forearm flexor surface. The en face numerical density of granular keratinocytes is greater on the face as compared with all other sites, whereas the surface density of spinous keratinocytes is greater on sun-protected sites. Additionally, the number of basal keratinocytes per millimeter length of dermoepidermal junction is greater in sun exposed areas. Interestingly, the dermal papillae shape varies and their sizes increase in circumference from sun-exposed to sun-protected sites, as observed at a specific depth below the stratum corneum. In summary, our results demonstrate that near infra-red reflectance confocal microscopy is a feasible tool for microscopic analysis of skin morphometry in vivo. (+info)
Elderly and sun-affected skin. Distinguishing between changes caused by aging and changes caused by habitual exposure to sun.
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OBJECTIVE: To review and distinguish between skin changes produced by aging and changes produced by habitual exposure to sun. QUALITY OF EVIDENCE: The literature was searched from 1969 to 1999 for articles on dermatoheliosis and sun-damaged skin. Surprisingly few were found comparing the difference between elderly skin and sun-damaged skin. A few articles focused on certain small aspects of sun-damaged skin. Many excellent articles described particular changes (e.g., actinic keratosis), but few covered all the changes due to aging and to sun. MAIN MESSAGE: Skin changes due to aging can be distinguished from those due to sun damage. All changes due to sun exposure can be grouped under the term dermatoheliosis; five parts of the skin are involved: epidermis (actinic keratosis), dermis (solar elastosis), blood vessels (telangiectasia), sebaceous glands (solar comedones), and melanocytes (diffuse or mottled brown patches). Habitual exposure to sun and a white skin are prerequisites for developing these changes. Knowing the difference between changes caused by sun and by aging can help physicians predict which patients are most likely to get skin cancers. CONCLUSION: Knowledge of these common skin changes will help physicians diagnose and manage the skin abnormalities of elderly people and of people with dermatoheliosis. (+info)
Vitamin D deficiency and insufficiency in Orthodox and non-Orthodox Jewish mothers in Israel.
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BACKGROUND: The modest clothing that Orthodox Jewish women wear exposes very little of their skin to sunlight. Under these conditions they may develop vitamin D deficiency, even in sunny Israel. OBJECTIVES: To determine and compare the vitamin D nutritional status in Jewish orthodox mothers to that of non-orthodox mothers who live in the same metropolitan area in Israel. METHODS: 25-Hydroxyvitamin D was measured by competitive protein-binding radioassay in the sera of 341 Jewish Israeli mothers (156 orthodox and 185 non-orthodox). The sera were obtained 48-72 hours after childbirth during the late summer of 1998 and the spring of 1999. RESULTS: The mean (SD) serum concentration of 25-OHD was significantly (P < 0.002) lower (13.5 +/- 7.5 ng/ml) in the orthodox than in the non-orthodox mothers (18.6 +/- 9.6 ng/ml). Vitamin D deficiency (< 5 ng/ml) and insufficiency (< 10 ng/ml) were more common in the orthodox mothers (5.1% and 32.7% respectively) than in the non-orthodox mothers (2.7% and 13%, respectively). In subgroups of mothers supplemented with 400 units of vitamin D daily during pregnancy, vitamin D deficiency and insufficiency were less common (2.2% and 13%, respectively) in orthodox and non-orthodox mothers (0% and 8.1%, respectively). Vitamin D insufficiency was more common in the winter than in the summer only among non-orthodox mothers. CONCLUSIONS: The high prevalence of vitamin D deficiency and insufficiency in Israeli mothers raises the question whether vitamin D supplements should be given to pregnant women in Israel, at least to orthodox mothers. (+info)
Can skin wrinkling in a site that has received limited sun exposure be used as a marker of health status and biological age?
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OBJECTIVES: to determine if skin wrinkling in a site that had received limited sun exposure may be a marker of health status and biological age. DESIGN: population-based, cross-sectional study. PARTICIPANTS: we evaluated the health status of representative samples of elderly Greek-born people living in Melbourne, Greeks living in rural Greece, Anglo-Celtic Australians living in Melbourne and Swedes living in Sweden. We carried out microtopographic assessment of their skin and measured plasma dehydroepiandrosterone concentrations. METHODS: we derived activities of daily living, well-being, memory and general health status scores from a cross-cultural questionnaire. We measured skin wrinkling using cutaneous microtopographic methods and plasma dehydroepiandrosterone by enzyme immuno-assay. RESULTS: skin wrinkling was positively correlated with age (r(s)=0.27, P<0.0001) and negatively with body mass index (r(s)=-0.19, P<0.0001). Therefore, all analyses were controlled for these variables. Plasma dehydroepiandrosterone was higher in smokers than non-smokers (2.86 vs 2.08; P<0.001) and men had significantly higher plasma dehydroepiandrosterone than women (2.74 vs 1.69; P<0.0001). In the pooled data, skin wrinkling was negatively associated with general health score (r(s)=-0.13, P<0.01) and activities of daily living score (r(s)=-0.14, P<0.05) after controlling for age, body mass index and smoking. These associations were more pronounced in women. Finally, those with the least skin wrinkling had the highest dehydroepiandrosterone level (r(s)=-0.12, P=0.06) after adjusting for age, smoking and sex. CONCLUSION: skin wrinkling in a site with limited sun exposure might be used as a marker of health status and, to some extent, biological age--particularly for women. (+info)