ABSTRACT
This review article is based on a systematic literature search using Pubmed and keywords aging and senescence, interchangeably. Aging [senescence] is the progressive deterioration of many bodily functions. It may or may not be linked to disease, disability and loss of independence. Populations worldwide are aging. Theories of aging biology are interactive and interdependent. They fall into programmed theories and error or damage theories. Longevity genes are under scientific scrutiny, via utilising microarray technology, founder populations and centenarians' family history. Telomere shortening is another programmed theory to explain healthy senescence. Biochemistry of the endocrine theory includes hormonal deficiencies, growth factors and heat shock proteins. Immuno-senescence furthermore elaborates the programmable aging. Among many of error/damage theories are free radical theory, mitochondrial dysfunction, membrane hypothesis of aging, protein cross-linking and DNA repair and maintenance. Biomarkers of aging, as in senescence marker protein-30 and klotho protein, offer the feasibility for exploring aging biology and physiology, advancing our understanding of genetic and lifestyle contributions to aging, and, at best, developing effective age-defying interventions