Scottish Government

2 PHYSIOLOGICAL EFFECTS OF AGEING

Summary

This chapter provides an overview of the physiological consequences of ageing and the resultant impact this has on nutritional status and dietary intake.

It covers:

• Changes in weight as a result of ageing
• Changes in body composition and functional status as a result of ageing
• Changes in taste and smell as a result of ageing
• Impact of oral health and dentition on dietary intake

2.1 The older population is extremely diverse with large ranges in, not only age, but also levels of activity, fitness, frailty and dependency. In addition the ageing process per se, whether there is disease present or not, results in progressive and irreversible biological changes. It is associated with changes in body composition (i.e. changes in proportions of fat and muscle stores), a reduction in functional ability (i.e. ability to perform activities of daily living), altered sense of taste and smell and changes in the status of teeth. These changes impact individually and collectively on a person's ability to meet their nutritional requirements and thus their optimum nutritional status. It is, therefore, important to review the implications of these changes as this provides context when reviewing barriers to, and interventions for, older people meeting their nutritional requirements.

Weight changes and BMI in older people

2.2 Weight alone is a poor marker of nutritional status as it does not take into account a person's height. In view of this, weight is usually converted to Body Mass Index (weight (kg)/height (m ²)). The standard World Health Organisation ( WHO, 2009) classifications for BMI are shown in Table 2.1.

Table 2.1. BMIClassification in adults

WHO (2009) http://www.who.int/bmi/index.jsp?introPage=intro_3.html accessed 20.1.09

2.3 Despite BMI being regularly used as a marker of nutritional status it is only a crude marker of nutritional status and does not take into consideration body composition or where fat is stored. This is important as visceral abdominal fat (i.e. fat stored around the abdominal area) is associated with increased risk of cardiovascular disease and type 2 diabetes (Cook et al., 2005; Grant et al., 2007).

2.4 Despite the older population being extremely heterogeneous there are clear trends identifiable in weight loss and weight gain which occur in advancing age.

Weight gain

2.4.1 Weight gain resulting in overweight and/or obesity occurs when a person's energy intake exceeds their energy expenditure (through metabolism and daily activity). Older people expend less energy as a result of lower metabolic rates and changes in lifestyle with increased levels of sedentary behaviour (Phillips, 2003) resulting in weight gain. The levels of overweight and obesity (as measured by BMI) in adults in Scotland are shown in table 2.2.

Table 2.2: The prevalence of obesity in older people in Scotland

(Scottish Government 2009b)

Note

Overweight is a term used in clinical practice and is internationally recognised terminology to distinguish between BMI's of 25 - 30 (overweight) and BMI >30 (obese) as these are associated with differing health risks. These categories are discrete and not subsets of each other.

2.4.2 As can be seen in table 2.2. the incidence of levels of overweight and obesity generally increase with age. Alongside this there is an increased risk of a number of age-related disorders including type 2 diabetes, hypertension, cardiovascular disease and osteoporosis ( WHO, 2002). However, in the very old, increased BMI may have some protective effect. It has been demonstrated that in people aged 84-88 years mortality is increased when BMI is <22 kg/m ² but not when BMI is >30 kg/m ² i.e. obese (Rajala et al ., 1990). While, it is generally accepted that in the adult population a BMI range of 18.5 - 25kg/m ² is normal, this is not the case for an older person. Although the reason for this is not clear a review of good quality evidence by Beck and Ovesen (1998) suggest that a BMI of 24 - 29kg/m ² is healthy for most older adults. Together with Rajala et al .'s (1990) finding that higher BMI decreases the likelihood of mortality in the very old, there seems enough evidence to say that a higher BMI up to 29kg/m ² is acceptable for most people aged 70 years and over.

Weight loss

2.4.3 Weight loss is often seen in the older population and occurs as a result of wasting of body energy stores i.e. fat and muscle stores. Wasting is an involuntary loss of weight primarily caused by inadequate dietary intake which is often illness related. As people age their energy intake is often reduced and the National Diet and Nutrition Survey ( NDNS) of adults over 65 (Finch et al., 1998) found that in free-living older adults (i.e. those not living in institutions), mean daily energy intakes were lower than the Estimated Average Requirements for energy ( EARs). Reduction in food intake is caused by a variety of physiological, psychological, lifestyle and social factors leading to a reduced appetite, and/or a reduced ability to shop for or prepare food. This is discussed more fully in Chapter 5.

Discussion

2.5 There is a prevalence of overweight and obese people in the community as a whole. Being overweight or obese increases the risk of a number of age-related disorders including type 2 diabetes, hypertension, cardiovascular disease and osteoporosis ( WHO, 2002). Involuntary weight loss is associated with increased risk of falls, increased morbidity and increased mortality (Alibhai et al., 2005). These all have implications on a person's level of dependence and an individual's ability to source and prepare food.

2.6 The implications for weight gain and weight loss are discussed more fully in Chapter 3.

Body composition and functional status as a result of ageing

2.7 As people age there are significant changes in body composition. There is an increase in fat mass and a reduction in lean body mass (usually muscle). This process is accelerated after the age of 60 years of age and fat mass continues to increase until around the age of 75 years (Kyle et al., 2001). Alongside this overall increase in fat mass, there are changes to body fat distribution, with an increase in visceral abdominal fat. The changes in body composition may not impact on weight and do occur whether BMI changes or not.

2.8 The reduction in muscle mass (known as sarcopenia) is primarily a result of losses from skeletal muscle and these losses significantly compromise functional ability and strength (Payette et al., 1998). A 10% reduction in muscle mass has been shown to decrease functional ability, increase risk of infection and is also associated with increased levels of mortality (Broadwin et al., 2001; Landers et al., 2001). In addition this age-related muscle loss is strongly associated with impaired mobility, increased incidence of falls, increased morbidity and poorer quality of life (Baumgartner et al., 1998, Roubenoff, 2000). These effects will determine a person's ability to live independently.

2.9 This loss in muscle mass and function also has an impact on a person's ability to chew food properly (particularly in frail older people) thus limiting food choice and contributing to an inadequate and poor quality dietary intake (Mioche et al., 2004). Some older people may therefore require texture modification of food (i.e. altering the texture of food to make it easier to chew or swallow).

Changes in taste and smell

2.10 As part of the ageing process there are a number of complex mechanisms which occur and result in deterioration in a person's sense of smell. This is not just an overall reduction in the ability to smell but also an inability to discriminate between smells. There is a reduction in sense of smell from early adulthood into old age (Drewnowski, 2001). This decline continues in advancing age with a considerable loss of ability over the age of 70 and with more than 75% of people over the age of 80 years having evidence of major impairment in their sense of smell (Boyce & Shone, 2006). This may impact on a person's enjoyment of food, may reduce the appetising effect of food and may result in a decreased dietary intake.

2.11 Taste changes are less prevalent than changes in ability to smell and indeed what is often perceived as a change in taste is in fact a result of decreased ability to smell (Boyce & Shone, 2006). However, some taste changes do occur in older people with perception of bitter showing the greatest decline and sweet the least. In addition age-related loss in taste sensitivity is most noticeable in individuals on medication with a significant number of those commonly prescribed in older people being a particular problem e.g. antibiotics, antihypertensives, analgesics, anti-depressives. Exacerbating this further is the likelihood that older people are in receipt of multiple prescriptions for medications (Schiffman & Graham, 2000).

Oral health

2.12 The National Diet and Nutrition Survey for people over 65 (Finch et al ., 1998) found that more older people had fewer of their own teeth with only 35% of people over 75 having any teeth of their own. Those people without their own teeth reported greater difficulty with chewing, more mouth dryness, a more restricted diet and thus had lower energy and micronutrient intakes compared to people of the same age who had their own teeth (Steele, 1998).

2.13 Many older people wear dentures and as weight changes there is an impact on how well the dentures fit. Older people who experience significant weight loss and frail older people commonly have poorly fitting dentures which impacts on their ability to chew foods properly and this causes a decrease in dietary intake and reduces the variety of foods available further exacerbating weight loss (Ritchie et al ., 2000).

2.14 The oral health status of the UK population is changing rapidly with increasing numbers of people retaining their own teeth. It is predicted that this pattern will gradually spread in the next 20 - 30 years and will impact on rates of dental diseases in the older population (Stanner et al., 2009). This change in dental status along with increasing numbers of older people may have a significant impact on dental service provision with increasing demands being placed upon it.

Key findings

• Both weight gain and weight loss can lead to poorer health in older people.
• Ageing is associated with loss of muscle stores and increases in fat stores which can lead to a decline in functional ability and strength.
• Ageing is associated with increasing levels of chronic illness and disease which can lead to and exacerbate poor nutritional status.
• A high BMI is associated with less risk than a low BMI in 'older' old people.
• A BMI of 24-29kg/m ² can be considered healthy in older people aged 70 years and over.
• A 10% reduction in muscle mass has been shown to decrease functional ability, increase risk of infection and increase risk of mortality.
• The texture and flavour of food may be particularly important for some older people to enable them to meet their nutritional requirements.
• There is a deterioration in taste, smell and the state of teeth with increasing age and these impact on dietary intake and nutritional status.
• Greater numbers of older people will retain their own teeth over the next 2-3 decades and this along with increasing numbers of older people may have a significant impact on the provision of dental services with increasing demands being placed upon it.