Chronological aging

Chronological Age. Because of this wide variation within the elderly population, it is difficult to devise a catch-all age one must attain to be considered elderly. Within the government, there also appears to be a problem of consistently defining this age group. Table 2, which lists a variety of federally funded programs and their corresponding age criteria, illustrates this point quite well. Table 3 lists what seems to be one of the better classification systems that has been devised [5], As well as being the system currently used by the U.S. Bureau of the Census, it is often implemented in studies that specifically deal with elderly populations [6,7]. 

Figure 27. Radiocarbon age vs. chronological age of tree rings vs. years 4000—...

Generally, larger cancers have a worse prognosis than smaller cancers. However, at least for some malignancies, size is a relatively weak indicator of outcome and is probably an indicator more of the chronological age of the tumor than of aggressiveness. Furthermore, size can be difficult to determine accurately when tumors have poorly defined infiltrating borders. 

After Helfman and Bada [143] found that a very good correlation exists between chronological age and racemization ratio of aspartic acid, as compared to the other amino acids, in dentin of teeth, a number of methods, mainly based on GC separation, have been published. 

Thyroid hormone also plays a major role in the maturation of bone. A deficiency of thyroid hormone in early life leads to both delay in and abnormal development of epiphyseal centers of ossification (epiphyseal dysgenesis). Hypothyroidism-induced impairment of linear growth can lead to dwarfism in which the Umbs are disproportionately short in relation to the trunk with the apparent bone age retarded in relation to chronological age. 

A 9-year-old boy with early puberty took oxandrolone for 22 months because of constitutional delay of growth. His height velocity increased above the 97th percentile and his bone age developed twice as fast as his chronological age. The oxandrolone was withdrawn, but his growth velocity did not decrease and his bone age continued to accelerate. 

Qiu S., Pak C. W., and Curras-Collazo M. C. (2006). Sequential involvement of distinct glutamate receptors in domoic acid-induced neurotoxicity in rat mixed cortical cultures effect of multiple dose/duration paradigms, chronological age, and repeated exposure. Toxicol. Sci. 89 243-256. 

Zouboulis, C.C. and Boschnakow, A., Chronological ageing and photoageing of the human sebaceous gland, Clin. Exp. Dermatol., 26, 600-607, 2001. 

Zettersten, E.M., Ghadially, R., Feingold, K.R., Crumrine, D., and Elias, P.M., Optimal ratios of topical stratum corneum lipids improve barrier recovery in chronologically aged skin, J. Am. Acad. Dermatol., 37, 403 108, 1997. 

Chronic inflammation causes premature aging of the skin, as observed in patients with atopic dermatitis. The constant inflammatory process leads to decreased function of the skin barrier, accompanied by loss of skin moisture. Presumably, the skin of such patients contains decreased levels of HA. Alternatively, the HA may reflect that found in chronological aging, with a change in the ability to take on water of hydration with enhanced association with tissue structures and loss of extractabil-ity. Demonstration of such changes and the precise histolocalization of this decreased HA deposition would be of intrinsic interest, a study that has not been performed yet. 

D. Chlubek, I. Nocen, E. Dabkowska, B. Zyluk, Z. Machoy, B. Kwiatkowska, Fluoride accumulation in human skulls in relation to chronological age, Fluoride 29 (3) (1996) 131-134. 

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