Normally, nutritional requirements do not change with age; but changes in lifestyle, eating habits, disease, and income will directly affect nutrition and health. Even though nutritional requirements do not change, caloric requirements do. For each decade after 50, the caloric requirements are reduced by 10%. This rate is associated with changes in metabolic rates, body mass, activity levels, and exercise tolerance.
Several factors combine to cause a greater need for calcium. Some degree of osteoporosis is normal, but a sedentary lifestyle compounds the problem. The rate of bone loss decreases if calcium levels are kept elevated, which can be done through exercise, diet, and supplementation.
The elderly are also more likely to require Vitamin D3 supplementation if they are to absorb the calcium efficiently. Because of skin changes and an increased intolerance for heat and exercise, many elderly avoid the sun. This slows sun damage to the skin, but also eliminates the natural production of vitamin D3. This vitamin is converted to the hormone calcitriol, which stimulates calcium absorption by the small intestine.
Maintaining a healthy diet becomes more difficult as a result of changes in the senses of smell and taste and in the restructure of the digestive system. With age, the senses of smell (olfactory) and taste (gustatory) declines. This can lead to dietary changes that ultimately affect the entire body. Since the number and sensitivity of olfactory and gustatory receptors decreases, food becomes less appealing. In addition, the mucosal lining of the digestive tract becomes thinner so that nutrient absorption becomes less efficient.
Secretion of saliva and digestive enzymes also decreases, causing a decrease in overall digestive abilities. Lesser secretions also impair the absorption of vitamins, particularly B12, and such minerals as iron and calcium.
As with other organs, the liver also shrinks during aging, thereby receiving a smaller supply of blood. This starts a domino effect – the rate of detoxification by the liver declines, thus prolonging the effects of drugs, which then predisposes the elderly to drug overdose. By age 70, the weight of the liver has decreased to 81% of previous capacity.
The rate of protein synthesis also decreases with age, as does the synthesis of digestive enzymes. Therefore, it is advisable for the elderly to eat more easy-to-digest proteins, that is, more plant-based proteins and less of the animal-derived products.