Nutritional and Metabolic Disorders
Nutriology as per Dorland’s Medical Dictionary is the science of nutrition. It is the science of how the body utilizes food to meet requirements for development, growth, repair, and maintenance. Nutrients are biochemical substances that can be supplied only in adequate amounts from an outside source, usually from food.
The relationship between nutrition and oral health is multifaceted. Nutrition has both local and systemic impacts on the oral cavity. While diet and eating patterns have a local effect on the teeth, saliva and soft tissues, the systemic impact of nutrition also has considerable implications and it too merits assessment as a component of comprehensive care. The systemic effect is the impact of the nutrients consumed as they assume their biological functions in relation to the development and maintenance of the extra- and intraoral structures and secretions. The oral cavity is often one of the first sites where nutrient deficiencies can be clinically noted.
Clinical manifestations of nutrient deficiencies can have a significant impact on the function of the oral cavity. Functional properties of the oral cavity include taste, salivation, mastication and swallowing food. Any alterations in the structure and function of the oral cavity may compromise intake and contribute to the development of a nutrient-deficiency state. When the associated oral structures are affected, these alterations may be compounded even further, leading to subsequent inadequate dietary intake and compromised nutritional status.
There are six classes of nutrients: water, carbohydrates, proteins, fats, minerals and vitamins. Nutrients work together and interact in complex metabolic reactions. Proteins, carbohydrates and fats provide energy for body needs. However, the body cannot use this energy without adequate amounts of vitamins and minerals.
Energy requirement is defined as the amount that will balance the energy expenditure of the individual (as determined by body size and composition and level of physical activity) consistent with long-term good health. This intake will allow for the maintenance of economically necessary and socially desirable physical activity. In children and pregnant/lactating women, the energy requirement will include energy needed for deposition of tissue and secretion of milk at the rate consistent with good health. All estimates of requirement are based on habitual intakes though these are expressed as daily intake.
Recommended dietary allowance (RDA) is the amount of selected nutrients considered adequate to meet the known nutrient needs of healthy people. The Canadian equivalent is the recommended nutrient intakes (RNIs). The energy needs of men and women for different activity levels computed on the basis of recommendations made by a Joint Expert Consultation of the World Health Organization (WHO)/Food and Agricultural Organization (FAO)/United Nations University (UNU) in 1985 and by an Expert Committee constituted in 1988 by the Indian Council of Medical Research (ICMR) are as shown in Tables 1 and 2. The ICMR’s RDA is higher than those recommended by the WHO/FAO/UNU.
Source: Dr BS Narasinga Rao–Gopalan Oration (2001).
Source: *WHOIFAO/UNO (1985); †ICMR (1988).
For computing RDA, the ICMR has taken body weight of ‘reference man’ as 60 kg and that of ‘woman’ as 50 kg. Average weight of Indian men is 52 kg and women 44 kg. For children and adolescents, weight for age from National Center for Health Statistics (NCHS), USA/well-to-do Indian children have been utilized by ICMR for deriving the RDA so that energy intake enables optimum growth. However, as in adults, majority of children and adolescents weigh substantially less and hence their energy requirement is lower.
Carbohydrates have been the major sources of energy since the dawn of history and furnish up to 90% of energy needs. Carbohydrates provide about 4 kcal/g. The average adult stores about 300 g of carbohydrate in the liver and muscle tissue as glycogen.
Grains (wheat, corn, rice, oats, rye, barley, buckwheat and millet) provide complex carbohydrates and starches. Vegetables, especially root and seed varieties (potatoes, sweet potatoes, beet and peas) contain considerable amounts of starch. Milk is a good source of lactose. Dietary fiber can be obtained from whole grain breads and cereals and legumes.
For decades, dietary carbohydrates have one of the major constituents incriminated in the causation of caries. The occurrence of caries depends upon the frequency of consumption, chemical constitution, route of administration, and physical properties of carbohydrates.
Sugar substitutes have been claimed to be non-cariogenic due to their inability to act as substrates for the enzyme glucosyltransferase. Xylitol is one such commonly used sugar substitute. It has been found to be non-cariogenic. Some studies also show that chewing xylitol gum has cariostatic properties. Other sugar substitutes, sorbitol, aspartame, sucralose have been found to have a negligible effect on the development of caries.
Second to water, proteins are the most abundant substances in the body. The structural units of proteins are amino acids. Of the 20 amino acids present in nature, nine are considered essential, i.e. these are to be supplied by the diet.
Kwashiorkor occurs when a child is fed on a diet with very low protein content relative to energy. This results in a high level of plasma insulin and low levels of plasma cortisol. This hormonal pattern leads to an uptake of amino acids in muscle, diverting these from liver, leading to decreased albumin synthesis and therefore edema.
Thus a child with kwashiorkor shows apathy, lethargy and severe anorexia. There is generalized edema, muscle wasting in shoulders and upper arms. The child may have a ‘moon face’. Potbelly due to weakness of abdominal muscles occurs. Skin changes in the form of thickening, cracking and areas of denudation occur. Hair changes color and becomes sparse.
Marasmus occurs when there is inadequate food intake resulting in energy deficiency. This leads to low insulin and high plasma cortisol levels. This results in amino acids being released from muscles making them available for protein synthesis.
During tooth development, mild-to-moderate protein deficiency results in smaller molars, chemical alterations of the exposed enamel surface, significantly delayed eruption and retardation of mandibular development. Smaller salivary glands develop resulting in decreased salivary flow. This saliva has a different protein, amylase and aminopeptidase activity, thereby compromising its immune function. Delayed eruption and decreased salivary flow lead to increased incidence of dental caries. Epithelium, connective tissue and bone may be poorly developed. Insufficient intake of protein results in negative nitrogen balance, decreased levels of secretory IgA. This leads to a lowered resistance to infections, reduced ability to withstand the stresses of injury or surgery, and prolonged recovery time. PEM may be a major reason for the occurrence of necrotizing ulcerative gingivitis (NUG) and noma.
Polyunsaturated fatty acids (PUFAs) contain two or more double bonds. Three PUFAs that are considered to be essential fatty acids include linoleic, linolenic and arachidonic acids. These are found in safflower, soybean, fish and corn oils, nuts and seeds.
Over consumption of fats leads to excessive fat stores and obesity. Other conditions related to fat consumption include diabetes mellitus, hyperlipidemia, fatty infiltration of liver, and certain types of cancer.
These are soluble in fats or fat solvents. Chemically, these are organic substances and do not contain nitrogen. These are absorbed in the intestines in the presence of bile. These are fairly stable to heat, as in cooking. Larger amounts of these vitamins can be stored in the body and for long periods of time. Thus, symptoms of deficiencies appear late. Increased intake may lead to toxicity.
Vitamin A (retinol) is an essential nutrient needed in small amounts by humans for the normal functioning of the visual system; growth and development; and maintenance of epithelial cellular integrity, immune function, and reproduction. These dietary needs for vitamin A are normally provided as preformed retinol (mainly as retinyl ester) and provitamin A carotenoids or β-carotene.
Vitamin A functions at two levels in the body: the first is in the visual cycle in the retina of the eye; and the second is in all body tissues where it systemically maintains the growth and soundness of cells.
In the visual system, carrier bound retinol is transported to the retina. Rhodopsin, the visual pigment critical to dim-light vision, is formed in rod cells after conversion of all-trans-retinol to retinaldehyde, isomerization to the 11-cis-form, and binding to opsin. Alteration of rhodopsin through a cascade of photochemical reactions results in the ability to see objects in dim light. The speed at which rhodopsin is regenerated is related to the availability of retinol. A deficient intake of vitamin A thus leads to night blindness.
The growth and differentiation of epithelial cells throughout the body is especially affected by vitamin A deficiency. In addition, goblet cell numbers are reduced in epithelial tissues and as a consequence, mucous secretions (with their antimicrobial components) diminish. Cells lining protective tissue surfaces fail to regenerate and differentiate, hence they flatten and accumulate keratin. Both factors—the decline in mucous secretions and loss of cellular integrity—reduce the body’s ability to resist invasion from potentially pathogenic organisms. Pathogens can also compromise the immune system by directly interfering with the production of some types of protective secretions and cells. Classical symptoms of xerosis (drying or non-wettability) and desquamation of dead surface cells as seen in ocular tissue (i.e. xerophthalmia) are the external evidence of the changes also occurring to various degrees in internal epithelial tissues.
Current understanding of the mechanism of vitamin A action within cells outside the visual cycle is that cellular functions are mediated through specific nuclear receptors. Binding with specific isomers of retinoic acid (i.e. all-trans-and 9-cis-retinoic acid) activates these receptors. Activated receptors bind to DNA response elements located upstream of specific genes to regulate the level of expression of those genes. These retinoid-activated genes regulate the synthesis of a large number of proteins vital to maintaining normal physiologic functions. There may, however, be other mechanisms of action that is as yet undiscovered.
To express the vitamin A activity of carotenoids in diets on a common basis, a Joint FAO/WHO Expert Group in 1967 introduced the concept of the retinol equivalent (RE) and established the following relationships among food sources of vitamin A:
|Group||Mean requirement (mg RE/day)||Recommended safe intake (mg RE/day)|
|Infants and children|
Source: Vitamin and mineral requirements in human nutrition, WHO.
Vitamin A is necessary for growth of both soft tissue and bone. It is required for resorption of old bone and synthesis of new bone, formation of ameloblasts, odontoblasts, and maintenance of the integrity of epithelial tissues.
Severe deficiency of vitamin A may result in enamel hypoplasia and defective dentin formation in developing teeth. Odontoblasts lose the ability to arrange themselves in normal parallel linear formation leading to altered dentin deposition. This further leads to degeneration and atrophy of ameloblasts. This results in enamel hypoplasia characterized by defects in enamel matrix and incomplete calcification.
Carotenoids possess antioxidant properties and are very efficient in scavenging singlet oxygen and peroxyl radicals. These free radicals are known to damage the structure and function of cell membranes. Thus a diet rich in antioxidants is associated with a lower risk of cancer and heart disease.
Stich and colleagues gave large quantities of (β-carotene and sometimes vitamin A to chewers of betel quids in Kerala, India, and to Canadian Inuits with pre-malignant lesions of the oral tract and witnessed reductions in leukoplakia and micronuclei from the buccal mucosa.
Retinoids have been used in oral precancer, cancer and immunologically mediated diseases such as lichen planus. Retinoids have a potent growth inhibiting effect on cancer in vivo and in vitro. They can induce apoptosis and regulate the function of the immune system. On this basis, retinoids have been used as chemopreventive agents in oral squamous cell carcinoma (SCC). However, clinical trials of retinoids have not yielded significant results. Retinoids have been used in the treatment of oral leukoplakia, and has been shown to cause temporary remission, but also causes toxicity. Retinoids have been used as an adjunctive treatment in the management of oral lichen planus. Retinoids eliminate reticular and plaque-like lesions but these recur following withdrawal of therapy.
Because vitamin A is fat soluble and can be stored, primarily in the liver, routine consumption of large amounts of vitamin A over a period of time can result in toxic symptoms, including liver damage, bone abnormalities and joint pain, alopecia, headaches, vomiting, and skin desquamation. Other clinical symptoms include diplopia, alopecia, dryness of mucous membranes, reddened gingiva, thinning of epithelium, cracking and bleeding lips, and increased activity of osteoclasts. Overconsumption of β-carotene leads to hypercarotenemia and yellow pigmentation of skin.
Vitamin D is required to maintain normal blood levels of calcium and phosphate, which are in turn needed for the normal mineralization of bone, muscle contraction, nerve conduction and general cellular function in all cells of the body. Vitamin D achieves this after its conversion to the active form 1,25-dihydroxy vitamin D (1,25-(OH)2D), or calcitriol. This active form regulates the transcription of a number of vitamin D-dependent genes that code for calcium-transporting proteins and bone matrix proteins. Vitamin D also modulates the transcription of cell cycle proteins, which decrease cell proliferation and increase cell differentiation of a number of specialized cells of the body (e.g. osteoclastic precursors, enterocytes, keratinocytes). This property may explain the actions of vitamin D in bone resorption, intestinal calcium transport and skin.
The most physiologically relevant and efficient way of acquiring vitamin D is to synthesize it endogenously in the skin from 7-dehydrocholesterol by sunlight (UV) exposure. In most situations, approximately 30 minutes of skin exposure (without sunscreen) of the arms and face to sunlight can provide all the daily vitamin D needs of the body (Table 4).
|Infants and children|
Source: Vitamin and mineral requirements in human nutrition, WHO.
Rickets is a clinical syndrome that occurs when there is a deficiency of vitamin D in the growing skeleton. Infants with rickets exhibit delayed development and muscle hypotonia, craniotabes (small non-calcified areas in skull bones), bossing of frontal and parietal bones, swelling of the rib costochondral junctions (rickety rosary). Severe rickets may be associated with hypocalcemic tetany, giving rise to laryngeal stridor when the vocal cords are affected.
Patients with rickets also have involvement of alveolar bone resulting in its weakening. Patients with severe vitamin D deficiency develops enamel hypoplasia. This is characterized by pitting of surface enamel. These surfaces are prone to adherence of plaque. However, studies of susceptibility to caries among these teeth reveal conflicting results.