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Essential vitamins and minerals are also known as micronutrients. While required in minute quantities, these nutrients are essential for life. They are uniquely required for essential biological and structural functions in the body, including as hormones, antioxidants, and enzyme cofactors and for one‐carbon metabolism and DNA synthesis. Because they cannot be synthesized in adequate quantities in the human body, they must be consumed from external sources such as foods, fortified or enriched foods, and/or dietary supplements. Vitamins are characterized as water‐soluble (e.g. B vitamins and vitamin C) or fat‐soluble (vitamins A, D, E, and K).

The shortfall in calorie and protein intake in many older adults is well recognized and the focus of considerable attention (see Chapters 12–14). Less appreciated is the concomitant risk of multiple micronutrient deficiencies. The same age‐associated changes in food intake that contribute to protein‐calorie inadequacies can also contribute to deficiencies of multiple micronutrients and are related to many different factors. These include age, psychological factors, physiological decrements, chronic disease, and medical factors.¹ Inadequate micronutrient intake can lead to suboptimal cellular and physiological functions even before developing a ‘classic’ and symptomatic deficiency syndrome.²

Age‐related causes of suboptimal diet intake include anorexia of ageing, decreased olfaction, and decreased taste ability. Social factors include poverty, isolation, lack of knowledge, low health literacy, difficulties with meal preparation, inability to shop, and lack of culturally appropriate foods in the community, hospital, assisted living, or long‐term care. Psychological factors related to low nutrient and energy intake include depression, bereavement, addiction (alcoholism), dementia, paranoia, mania, anorexia tardive, and sociopathy. Physiological and chronic health problems include difficulties chewing and/or swallowing, gastrointestinal disease, hepatic disease, renal disease, and some drug‐nutrient interactions. Gastrointestinal disorders may decrease absorption of nutrients, while renal disease may alter excretion of nutrients, and renal and/or liver disease may alter metabolism to active forms (e.g. conversion of vitamin D to an active form, 1,25‐dihydroxyvitamin D). Several medical factors of concern for insufficient nutrient and energy intake and/or status are summarized in Table 16.1.¹