Sunday, May 27, 2007

Why Do Old People Get Shorter?

Introduction

Adults start losing height in their 30s, due to many factors that lead to the deterioration of bones, muscles and joints. By age 70, a person has lost approximately 4cm; after age 70, height decreases at a significantly faster rate (Harvard). The rate of decrease in height is greater in women than in men (see figure 1).

Height changes normally occur along the trunk and spine. As there are no significant changes in the long bones of the arms and legs, height loss is primarily caused by shortening of the trunk and spine (A.D.A.M.).

Bone Deterioration

Both compact bone and spongy bone continue to be replaced in a process called remodeling. “Normally bone remodeling involves a process whereby old bone resorption is balanced by new bone formation, with (at least theoretically) no net loss of bone tissue” (Kiebzak p.173). But as people grow old, the remodeling sequence becomes dis-aligned, which means that resorption continues at the same rate as before but the speed of formation slows down, causing bone turnover to decrease, so that by about age 40 there is proportional bone loss as osteoclastic activity exceeds osteoblastic activity (Christiansen & Grzyybowshi, p.58).

Mineral-associated proteins, which exist in the extracellular matrix of the bone tissue, decrease with age. “Circulating levels of calcitonin may decrease with age and the calcitonin reserve may be impaired in the elderly” (Kiebzak p.178), and if so this would contribute to the degeneration of bone mass.

Loss of bone mass can lead to vertebral fractures, causing kyphosis and resulting in the spine hunching over. This fracturing can occur in the thoracic region of the spine or within the whole vertebrae region (Harvard). This is caused by the over- mineralization of the bone, which in turn results in the “crystallinity of bone increase with age” (Kiebzak p.176). This change in turn leads to an accumulation of micro-fractures as “mineralized tissue develops tiny cracks as a consequence of critical mechanical stress” (Kiebzak p.175).

Muscle and Connective Tissue Atrophy

“Voluntary muscle strength declines significantly in older adults. One contributing factor to this strength loss is muscle atrophy developed in old age”. Yue, et al. found that “the ability to maximally activate the muscle decreases with age.” As inactivity is a known cause of muscle loss, this inability to fully utilise the muscles must contribute to their gradual loss in older people.

In the very old, many of the limbs often cannot be completely extended because of decreased ligamental flexibility. This lack of extension results in a permanent stooped appearance and accentuates short stature (Christiansen & Grzyybowshi, p.59). Foot arches also become less pronounced with aging, causing slight height loss (A.D.A.M).

Progressive loss of muscle depends on the specific muscle and how much it is used. This loss is manifested by a decrease in the number of muscle fibres and by their shrinkage (A.D.A.M). Muscle tissue is replaced more slowly, and the aging muscle fibres are replaced with fat and collagen. (Christiansen & Grzyybowshi p.80).

Joint Wear

The trunk gets shorter as the intervertebral disks lose fluids and bones get thinner. This leads to the compacting of the vertebrae, and shrinkage in stature. “Disc thinning occurs due to loss of fluid content, conversion of the nucleus tissues to a highly organized collagenous tissue, gradual ossification of the end plate and protrusion of disc tissue” (Aebi, Gunzburg & Szpalski p.18). This loss of fluids in the joints also contributes to the wearing out of the cartilages.

“Older adults experience some major changes in the articular system, particularly in the synovial joints. Elastin and collagen fibers in an joint become less flexible and tissue repair declines. The articular cartilage surfaces wear and decline because older adults are not able to replace cartilage as quickly as when they are younger” (Rizzo p.10).

This is all likely to lead to the knees and hips becoming more flexed as they begin to lose structure due to the degenerative changes (A.D.A.M).

Additional Factors

Activity: Mechanical loadings (i.e. high density physical activities) are considered perhaps the most important factors in shifting the remodeling balance in favour of bone formation in adults. It is found that weight-bearing exercises can increase bone mass in the elderly (Kiebzak, p 178). However, it is also found that participation in these activities significantly decreases with age. Research has also established that inactivity results in a shrinkage of bone and muscle density.

Diet: The diet of the elderly frequently lacks minerals and vitamins, especially calcium (Kiebzak, p.178). Malnutrition in the elderly is considered to be often under-diagnosed (Wells & Dumbrell p.1). Lack of nutrition preventing optimal body function, combined with a lack of energy and mobility, results in overall body deteriation and therefore height reduction.

Case Study

Laura, 73, has lost 57cm of her height in 45 years. She measured 172 cm at age 28 and now she measures 115cm. She had an hysterectomy at age 28 and noticed her height reducing at approximately age 35. Her shrinkage appeared to slow when she undertook Hormone Replacement Therapy at 50. However, in the past six years, there has been a large decrease in height and her posture has become stooped. Recently, she was found to have osteoarthritis in the cervical vertebra and underwent a spinal fusion. Her noticeable height loss after the hysterectomy and the slowing down of her height loss after starting H.R.T. indicate that in this case the height loss is likely to be related to hormone levels.

Conclusions

Aging is a complex and varied process. Most gerontologists feel that height loss with age is the cumulative effect of many factors, including genetic, environmental and cultural influences, nutrition, exercise and general lifestyle (A.D.A.M).

The decrease in height that people experience as they reach old age can be ultimately attributed to normal wear and tear on cartilage and spinal disks, which leads to the cartilage being worn away from joints (typically knee) and compression of the spinal disks. The resultant pain precipitates reduced muscle usage, beginning a deteriorative cycle of reduced muscle size, decrease in bone density, thinner bones, and pain and inactivity take hold, thus leading to the shrinkage most elderly people undergo. Women shrink more than men, however, due most likely to hormonal changes.

Regular exercise is one of the best ways to slow or prevent problems with bones, muscles and joints. Tai chi and yoga can help in maintaining or improving muscle control, body balance and posture.

References:

• Aebi M, Gunzburg R, & Szpalski M (eds). (2005). The Aging Spine. Springer – Verlag Berlin Heidelberg .
• Christiansen, J L & Grzybowski, J M. (1993) Biology of Aging. Mosby –Year Book, Inc.
• Cohen, Sandra W. (2006). Aging changes in the bones- muscles- joints. A.D.A.M Navigator, Online health information and services, URAC accredited Health website.
• Harvard Health Letter (2005). Standing Tall. Expanded Academic ASAP. Thomson Gale. RMIT University Library Online Database. Dec Issue 2.
• Kiebzak G M. (1991) Age-related Bone Change. Experimental Gerontology. Vol 26, pp171-187.
• Rizzo DC. (2006) Fundamental of Anatomy and Physiology, 2nd ed. Thomson Delmar Learning
• Sorkin J D, Muller D C & Andres R. (1999). Longitudinal Change In the Heights of Men and Women. Epidemiologic Reviews. Vol 21, No.2.
• Wells, Jennie L, & Dumbrell, Andrea C. (2006) Nutrition and aging: assessment and treatment of compromised nutritional status in frail elderly patients. Clinical Interventions in Aging 1:1, 67
Yue, Guang H., Vinoth K. Ranganathan, Vlodek Siemionow, Jing Z. Liu, & Vinod Sahgal. (1999) Older adults exhibit a reduced ability to fully activate their biceps brachii muscle. The Journals of Gerontology, Series A 54.5, M249(5).”

5 Comments:

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University: RMIT Bundoora
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Semester: 1, 2007
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