In the beginning of the golden age of truth, Satya-yuga, also known as the Krita-yuga, human beings were endowed with divine vitality. Exceedingly faultless and unhampered in their powers, they had direct knowledge. These god-like sages knew the divine law, and the sacrificial rituals. They possessed bodies which were robust, compact and firm, and had clear senses and mind. Thye had good complexions and their speed, strength and power resembled those of the wind. They were free from desire, aversion, infatuation, greed, anger, pride, diseases, laziness, fatigue, languour and the spirit of aquisition. They experienced unlimited longevity. For the benefit of these people with heroic minds, qualities and deeds, their crops were replete with wonderful taste, potency, post digestive effects, specific actions and virtue, because the earth, during the sawn of the golden age was charged to the full with all excellent qualities.
During the latter part of the Satya-yuga, those whe were financially better off ate more and became obese. By over-indulgence this heaviness of body led to lassitude; lassitude gave rise to indolence, indolence created the need of accumulation and necessitated acquisition. The spirit of acquisition engendered greed. The qualities of earth also deteriorated gradually along with the qualities of human beings.
Thereafter, the bodies of human beings failing to receive nutrition as before from the progressively deteriorating quality of food, together with the lack of exercise and adverse effects of exertion, heat and wind, soon succumbed to attacks of fever and other dis-ease. Thereafter, in the second or silver age, known as the Treta-yuga, greed brought malice in its way and led to falsehood; falsehood bred lust, anger, vanity, hatred, cruelty, aggression, fear, grief, anxiety, distress and the like. Consequently in the second age, virtue found itself deprived of a quarter of its plentitude. From this quarterly loss in virtue, there followed a similar deterioration in the duration of the succeeding age and in the beneficial power of the earth and other elements. The consequence of this deterioration led to a corresponding deterioration in the purity, taste, potency, post-digestive effects, specific ation and quality of herbs. In this manner righteousness dwindled in each succeeding age by one quarter, and the proto-elements too suffered silimar deterioration till eventually the world would come to dissolution.
When a hundredth part of the length of an age period is past, then the life span of creatures gets less by one year. This is in reference to the normal determination of life span in a given age. Thus, not following the path of righteousness and not following the dictates of conscience are the root cause of all disease.