This is easily determined by the height ratio of any object to the size of its shadow (if the height is measured vertical to the earths gravitational field, the projected shadow is ideally measured on a flat, level surface; furthermore, for objects wider than skulls or poles, the height and length are best measured relative to the same occluding edge). The greatest risk is at solar noon, when shadows are at their minimum and the suns radiation passes most directly through the atmosphere. Regardless of ones latitude (assuming no other variables), equal shadow lengths mean equal amounts of UV radiation. The skin and eyes are most sensitive to damage by UV at 265–275 nm wavelength, which is in the lower UVC band that is almost never encountered except from artificial sources like welding arcs. Most sunburn is caused by longer wavelengths, simply because those are more prevalent in sunlight at ground level. Ozone depletion
In recent decades, the incidence and severity of sunburn have increased worldwide, partly because of chemical damage to the atmospheres ozone layer. Between the 1970s and the 2000s, average stratospheric ozone decreased by approximately 4%, contributing an approximate 4% increase to the average UV intensity at the earths surface. Ozone depletion and the seasonal "ozone hole" have led to much larger changes in some locations, especially in the southern hemisphere. Tanning
Suntans, which naturally develop in some individuals as a protective mechanism against the sun, are viewed by most in the Western world as desirable.
Glucose hydrogen breath test for bacterial overgrowth
Lactose hydrogen breath test for lactose intolerance
Sugar probes or 51Cr-EDTA to determine intestinal permeability. Obsolete tests no longer used clinically
D-xylose absorption test for mucosal disease or bacterial overgrowth. Normal in pancreatic insufficiency. Bile salt breath test (14C-glycocholate) to determine bile salt malabsorption. Schilling test to establish cause of B12 deficiency. Management
Treatment is directed largely towards management of underlying cause:
Replacement of nutrients, electrolytes and fluid may be necessary. In severe deficiency, hospital admission may be required for nutritional support and detailed advice from dietitians. Use of enteral nutrition by naso-gastric or other feeding tubes may be able to provide sufficient nutritional supplementation. Tube placement may also be done by percutaneous endoscopic gastrostomy, or surgical jejunostomy. In patients whose intestinal absorptive surface is severely limited from disease or surgery, long term total parenteral nutrition may be needed. Pancreatic enzymes are supplemented orally in pancreatic insufficiency. Dietary modification is important in some conditions:
Gluten-free diet in coeliac disease. Lactose avoidance in lactose intolerance. Antibiotic therapy to treat Small Bowel Bacterial overgrowth. Cholestyramine or other bile acid sequestrants will help reducing diarrhoea in bile acid malabsorption. See also
Fructose malabsorption
Protein losing enteropathy

References


== External links ==