Title: Ageing and Changes in Body Composition.

Key words: Obesity, adipose tissue, visceral fat, diabetes, osteoporosis, kyphosis, malnutrition, degenerative diseases, metabolism, nutritional assessment, anthropomorphic measurements, antioxidants

Date: August 1999

Category: 11. Life Changes

Type: Article

Author: Dr van Rhijn

Ageing and Changes in Body Composition.

 

Introduction

The body's composition inevitably changes dramatically with advancing age and this is clearly interrelated with health and function. The great variation in expression and uniformity of body changes is dependent on health and nutritional status, as discussed below.

Major Changes in Body Composition

There is a rising prevalence of increased body weight (total body fat1) and subsequent obesity2, and a decrease in lean body mass by about 3 kg per decade after age 50, resulting in 9-12% reduction in Basal Metabolic Rate. There is a shift of body fat from the periphery to visceral fat (typical male & female distribution) deposit accretion together with a decreased ability to oxidise fat3. This may cause glucose intolerance, raised blood insulin and increase the risk of diabetes4. Adipose tissue also accumulates more around the internal organs, a trend accelerated by the menopause. This fat distribution is associated with the increased incidence of cardiovascular disease5.

There is a gradual decline in muscle strength over time (0.5 – 1%/year), due to atrophy of the muscle fibres, compromising mobility and eventually independence. Cross-sectional and longitudinal studies indicate a relatively stable fat-free mass (FFM) for both genders6, with a continuous decreases in amounts of water, muscle (protein and potassium) and bone starting in the 6th and 7th decade of life7. The water content of the body decreases with age (more rapidly in women after 60 years of age) as well as the thirst sensitivity and capacity to concentrate urine. This can impair temperature regulation and increase susceptibility to dehydration.

There is an alteration in bone density due to demineralisation8, (starting at age 30) resulting in osteoporosis (accelerated after menopause9), increased risk of fractures, deformities of the spine (kyphosis) and bowing of the legs. The amount of bone present at maturity (peak bone mass) is a major determinant of the amount of bone present in later life. Numerous factors determine the rate of bone loss such as physical activity, hormone levels, drugs, nutritional status. There is also a slight lifetime loss of stature, due to disc space narrowing, of probably about 3cm in men and 5cm in women10, or 10-20 cm decline per decade after the age of 55.

Altered tissue elasticity and compressibility occur, along with trophic changes in skin, hair and nails. Oral disease (edentulousness, caries, infection, gum disease) is common in the elderly and results in difficulty in chewing and decreased food intake (nurtients), contributing to weight loss and malnutrition11. There is a need for better body compositional data in elderly subjects in order to establish improved reference data for this population group12.

Ageing is characterised by a universally progressive decline in vitality and an increase in vulnerability, resulting in a gradual degeneration and failure of homeostasis with an increased probability of death. Biological ageing is difficult to measure, but the physiological effectiveness (Nerve conduction, GFR and Cardiac index) decline with age. Several components of the immune system are known to be impaired (delayed type-hypersensitivity responses, reduced natural killer cells, T cells and T-helper cells) in the elderly, contributing significantly to increased morbidity and mortality13.

There is a decline in neuroendocrine regulation, with reduced functioning of several hormonal systems (ADH, FSH/LH and GH). There is also molecular ageing with genome (DNA, mitochondrial DNA) damage, probably due to oxidative destruction secondary to free radicals and reactive O2 species. Protein synthesis is slower with an increased chance of molecular defects.

Influencing factors

In any one old person, the co-existence of age-related physiological changes, chronic disease and the use of medication as well as social and environmental factors, can influence nutrient intake, absorption and deposition and consequently nutritional status14. There are numerous physical and psychological causes of malnutrition, contributing to the rapid changes in body composition and addressing these may slow down the rate of change. Multifactorial, physiological anorexia15, resulting in a decline in food intake with ageing and early satiation, makes it difficult to ingest large amounts of energy at any single meal16. In general, the rate of weight loss, both FFM and fat, is proportional to the energy deficit. Protein energy malnutrition, common in the elderly is a major prognostic indicator for mortality. There are significant decreases in total, high-density lipoprotein and low-density lipoprotein plasma cholesterol levels over time in both men and women17, which correlates with a decrease in total fat and cholesterol intakes.

Decreased physical activity may account for increased body fat and loss of muscle tone and mass, and is often secondary to a variety of degenerative and chronic diseases18. Food intake, and nutritional status may be hampered by poor vision (acuity, cataracts19), edentation (ability to chew), reduction of smell and taste20 and changes in absorption21 of nutrients as well as metabolism. Social (poverty) and psychological (depression) factors also affect nutritional status.

 

Nutritional Assessments

Body compositional changes are not uniform among the elderly and numerous environmental, genetic and nutritional factors can affect the rate of decline. Malnutrition in the elderly is common22, 23, frequently unrecognised24 and associated with a higher mortality and morbidity25. Anthropomorphic measurements (detecting muscle and fat wastage) are important predictors of ill health, functional impairment and mortality26, 27. It is therefore crucial to use an appropriate and validated nutritional assessment, such as the Mini Nutritional Assessment (NMA)28 to identify those at risk and quantify the severity of their malnutrition29 or dehydration.

Solving nutritional problems in the elderly can slow down changes in body composition. This is an enormous task, requiring a multidisciplinary30 approach involving health care professionals, governmental agencies, food industry and administrators alike. The value of supplementation in the elderly is now well documented31, 32, 33. Short-term measures to correct malnutrition should be followed up with advice and education aimed at preventing recurrence and encouraging healthy eating. Only once the causes have been identified34 can steps be undertaken to intervene clinically with preventative and therapeutic measures.

Even a simple intervention such as the administration of liquid preloads, one hour before a meal, may increase the amount of food and therefore nutrients consumed35. Dietary restriction (calories) is probably the most successful modifier of ageing, as well as promotion of antioxidant rich foods (or supplements) to keep inevitable oxidative damage to a minimum36. There is overwhelming evidence that nutritional support in the elderly shortens rehabilitation time from illness37, 38.

It is therefore important to ensure adequate hydration to ensure proper kidney function.

Conclusion

Age-related changes affect most faculties relating to selection, choice and biological processing of food, and changes in body composition are therefore multifactorial. Chronic disease can affect the retention39 or loss of water, making it difficult to quantify body composition among elderly, for which there is no universally suitable measuring method. Active nutritional management will help to improve quality of life and may turn out to be very cost effective, contributing to the reduction of the medical bill for the elderly40. Health professionals should have access to the necessary basic training, which will enable them to assess and meet the nutritional demands of elderly patients at risk of undernutrition.

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