The digestive system exerts a considerable influence on the efficiency and work capacity of the body, and acute and chronic illnesses of the digestive system are among the commonest causes of absenteeism and disablement. In this context, the occupational physician may be called upon in either of the following ways to offer suggestions concerning hygiene and nutritional requirements in relation to the particular needs of a given occupation: to assess the influence that factors inherent in the occupation may have either in producing morbid conditions of the digestive system, or in aggravating others that may pre-exist or be otherwise independent of the occupation; or to express an opinion concerning general or specific fitness for the occupation.
Many of the factors that are harmful to the digestive system may be of occupational origin; frequently a number of factors act in concert and their action may be facilitated by individual predisposition. The following are among the most important occupational factors: industrial poisons; physical agents; and occupational stress such as tension, fatigue, abnormal postures, frequent changes in work tempo, shift work, night work and unsuitable eating habits (quantity, quality and timing of meals).
Chemical Hazards
The digestive system may act as a portal for the entry of toxic substances into the body, although its role here is normally much less important than that of the respiratory system which has an absorption surface area of 80-100 m2 whereas the corresponding figure for the digestive system does not exceed 20 m2. In addition, vapours and gases entering the body by inhalation reach the bloodstream and hence the brain without meeting any intermediate defence; however, a poison that is ingested is filtered and, to some degree, metabolized by the liver before reaching the vascular bed. Nevertheless, the organic and functional damage may occur both during entry into and elimination from the body or as a result of accumulation in certain organs. This damage suffered by the body may be the result of the action of the toxic substance itself, its metabolites or the fact that the body is depleted of certain essential substances. Idiosyncrasy and allergic mechanisms may also play a part. The ingestion of caustic substances is still a fairly common accidental occurrence. In a retrospective study in Denmark, the annual incidence was of 1/100,000 with an incidence of hospitalization of 0.8/100,000 adult person-years for oesophageal burns. Many household chemicals are caustic.
Toxic mechanisms are highly complex and may vary considerably from substance to substance. Some elements and compounds used in industry cause local damage in the digestive system affecting, for example, the mouth and neighbouring area, stomach, intestine, liver or pancreas.
Solvents have particular affinity for lipid-rich tissues. The toxic action is generally complex and different mechanisms are involved. In the case of carbon tetrachloride, liver damage is thought to be mainly due to toxic metabolites. In the case of carbon disulphide, gastrointestinal involvement is attributed to the specific neurotropic action of this substance on the intramural plexus whilst liver damage seems to be more due to the solvent’s cytotoxic action, which produces changes in lipoprotein metabolism.
Liver damage constitutes an important part of the pathology of exogenic poisons since the liver is the prime organ in metabolizing toxic agents and acts with the kidneys in detoxication processes. The bile receives from the liver, either directly or after conjugation, various substances that can be reabsorbed in the enterohepatic cycle (for instance, cadmium, cobalt, manganese). Liver cells participate in oxidation (e.g., alcohols, phenols, toluene), reduction, (e.g., nitrocompounds), methylation (e.g., selenic acid), conjugation with sulphuric or glucuronic acid (e.g., benzene), acetylation (e.g., aromatic amines). Kupffer cells may also intervene by phagocytosing the heavy metals, for example.
Severe gastro-intestinal syndromes, such as those due to phosphorus, mercury or arsenic are manifested by vomiting, colic, and bloody mucus and stools and may be accompanied by liver damage (hepatomegalia, jaundice). Such conditions are relatively rare nowadays and have been superseded by occupational intoxications which develop slowly and even insidiously; consequently liver damage, in particular, may often be insidious too.
Infectious hepatitis deserves particular mention; it may be related to a number of occupational factors (hepatotoxic agents, heat or hot work, cold or cold work, intense physical activity, etc.), may have an unfavourable course (protracted or persistent chronic hepatitis) and may easily result in cirrhosis. It frequently occurs with jaundice and thus creates diagnostic difficulties; moreover, it presents difficulties of prognosis and estimation of the degree of recovery and hence of fitness for resumption of work.
Although the gastro-intestinal tract is colonized by abundant microflora which have important physiological functions in human health, an occupational exposure may give rise to occupational infections. For example, abattoir workers may be at risk to contract a helicobacter infection. This infection may often be symptomless. Other important infections include the Salmonella and Shigella species, which must be also controlled in order to maintain product safety, such as in the food industry and in catering services.
Smoking and alcohol consumption are the major risks for oesophageal cancer in industrialized countries, and occupational aetiology is of lesser importance. However, butchers and their spouses seem to be at elevated risk of colorectal cancer.
Physical Factors
Various physical agents may cause digestive system syndromes; these include direct or indirect disabling traumata, ionizing radiations, vibration, rapid acceleration, noise, very high and low temperatures or violent and repeated climatic changes. Burns, especially if extensive, may cause gastric ulceration and liver damage, perhaps with jaundice. Abnormal postures or movements may cause digestive disorders especially if there are predisposing conditions such as para-oesophageal hernia, visceroptosis or relaxatio diaphragmatica; in addition, extra-digestive reflexes such as heartburn may occur where digestive disorders are accompanied by autonomic nervous system or neuro-psychological troubles. Troubles of this type are common in modern work situations and may themselves be the cause of gastro-intestinal dysfunction.
Occupational Stress
Physical fatigue may also disturb digestive functions, and heavy work may cause secretomotor disorders and dystrophic changes, especially in the stomach. Persons with gastric disorders, especially those who have undergone surgery are limited in the amount of heavy work they can do, if only because heavy work requires higher levels of nutrition.
Shift work may cause important changes in eating habits with resultant functional gastro-intestinal problems. Shift work may be associated with elevated blood cholesterol and triglyceride levels, as well as increased gamma-glutamyltransferase activity in serum.
Nervous gastric dyspepsia (or gastric neurosis) seems to have no gastric or extragastric cause at all, nor does it result from any humoral or metabolic disorder; consequently, it is considered to be due to a primitive disorder of the autonomic nervous system, sometimes associated with excessive mental exertion or emotional or psychological stress. The gastric disorder is often manifested by neurotic hypersecretion or by hyperkinetic or atonic neurosis (the latter frequently associated with gastroptosis). Epigastric pain, regurgitation and aerophagia may also come under the heading of neurogastric dyspepsia. Elimination of the deleterious psychological factors in the work environment may lead to remission of symptoms.
Several observations point to an increased frequency of peptic ulcers among people carrying responsibilities, such as supervisors and executives, workers engaged in very heavy work, newcomers to industry, migrant workers, seafarers and workers subject to serious socio-economic stress. However, many people suffering the same disorders lead a normal professional life, and statistical evidence is lacking. In addition to working conditions drinking, smoking and eating habits, and home and social life all play a part in the development and prolongation of dyspepsia, and it is difficult to determine what part each one plays in the aetiology of the condition.
Digestive disorders have also been attributed to shift work as a consequence of frequent changes of eating hours and poor eating at workplaces. These factors can aggravate pre-existing digestive troubles and release a neurotic dyspepsia. Therefore, workers should be assigned to shift work only after medical examination.
Medical Supervision
It can be seen that the occupational health practitioner is faced with many difficulties in the diagnosis and estimation of digestive system complaints (due inter alia to the part played by deleterious non-occupational factors) and that his or her responsibility in prevention of disorders of occupational origin is considerable.
Early diagnosis is extremely important and implies periodical medical examinations and supervision of the working environment, especially when the level of risk is high.
Health education of the general public, and of workers in particular, is a valuable preventive measure and may yield substantial results. Attention should be paid to nutritional requirements, choice and preparation of foodstuffs, the timing and size of meals, proper chewing and moderation in the consumption of rich foods, alcohol and cold drinks, or complete elimination of these substances from the diet.