however, be real and substantial, and not merely apparent; for the duty to prove work-causation or work-aggravation imposed by existing law is real x x x not merely apparent.[41]   The burden is clearly upon Masangcay to present substantial evidence, or such relevant evidence which a reasonable mind might accept as adequate to justify a conclusion, showing a reasonable connection that the nature of his employment or working conditions between the conditions of his work and his illness, i.e., renal failure, uremia[42] and/or nephrolithiasis[43]; or that the risk of contracting the same was increased by his working conditions. This, he did not do. If truth be told, Masangcay does not even assert that his illness is workrelated and/or was, at the minimum, aggravated by his working conditions at the M/T Eastern Jewel.   There is no substantiation that the progression of his ailment was brought about largely by the conditions of his job as an oiler. His medical history and/or records prior to his deployment as an oiler in M/T Eastern Jewel were neither presented nor alluded to in order to demonstrate that the working conditions on board said vessel increased the risk of contracting renal failure, chronic or otherwise.   To demonstrate just how bare the records are with respect to the illness with which Masangcay is allegedly afflicted, we cannot even make a definitive statement whether he had merely been afflicted with renal stones, or he is suffering from the more serious disease of chronic renal failure. The two physicians who issued their respective medical certificates have conflicting findings.   But even assuming that Masangcay is suffering from chronic renal failure, it still does not entitle him to compensation and benefits for a permanent disability.   In Harrisons Principles of Internal Medicine,[44] chronic renal failure is described as a result of progressive and irreversible destruction of nephrons, regardless of cause (citation omitted).[45] This diagnosis implies that glomerular filtration rate (GFR) is known to have been reduced for at least 3 to 6 months. Often a gradual decline in GFR occurs over a period of years.[46] It is, therefore, highly improbable that Masangcays chronic renal failure developed in just a