In a mortality study among seafarers in British merchant shipping 1976-1995 gastrointestinal disease was the second largest cause of death (after cardiovascular diseases), with 9% out of a total of 600 deaths, largely due to liver cirrhosis and stomach ulcers (14 each) and acute pancreatitis (7) [2]. Many were linked to lifestyle factors, and several of these diseased were also suffering from delirium tremens and other alcohol-related problems. A large proportion of fatal gastrointestinal disease (42%) was found in catering crew and stewards, a rank previously identified with frequent alcohol use [22]. However, Roberts [2] pointed out that heavy alcohol consumption at sea has declined in recent years; in particular following the implementation of screening after the grounding of the tanker Exxon Valdez resulting in a major oil pollution disaster off Alaska in 1989.

 Studying work-related mortality among British seafarers employed in flags of convenience shipping 1976-95, Roberts [3] found that out of a total of 200 deaths, illnesses caused 68 deaths, of which seven were from gastrointestinal disease (liver cirrhosis, acute pancreatitis, peptic ulcer, kidney failure, ruptured gall bladder and hepatitis [two]).

 In a study on work-related mortality among seafarers who were employed in British merchant shipping from 1939 to 2002, with a population of 7.29 million seafarer-years at risk, 864 deaths were from gastrointestinal diseases and 72 from alcoholism [1]. Overall mortality from gastrointestinal diseases fell from 18.4 per 100,000 in 1939-49 to 9.3 in 1970-79 and 0.3 in 1990-2002. Mortality from alcoholism, and from alcohol-related diseases such as liver cirrhosis and diseases of the pancreas, increased up to the 1960s or 1970s, but fell thereafter. At the time of the last censuses of seamen in 1961 and 1971, compared with the general British male working aged population, mortality among British seafarers was greatly increased for peritonitis and alcoholism but not for most other gastrointestinal diseases. The author concluded that sharp reductions in mortality from gastrointestinal diseases and from alcoholism since the 1970s contrasts with increases among the general British population, and are largely because of the “flagging-out” of most British deep sea ships, and consequent reductions in long voyages, as well as reduction in alcohol consumption among seafarers at work. Largely because of the healthy worker effect, seafarers were usually only at increased risks from particularly acute diseases, like peritonitis. Mortality from gastrointestinal diseases was similar among British and Asian seafarers in the British fleet during the 1940s, but it was almost twice as high among Asian seafarers from 1950-72, particularly for peptic ulcer, liver disease and peritonitis. Roberts speculated that this may be related to a higher prevalence of heliobacter pylori and hepatitis infections among Asian seafarers.

However, an important limitation of longitudinal mortality studies is that death certification would have improved over time, but it may be quite unreliable in the earlier years of the studies when sea burials were quite common, particularly on long inter-continental voyages, and at a time when more deaths occurred in foreign countries with less chance of an autopsy being undertaken [1]. There have also been substantial improvements in diagnostic techniques over time, and pre-employment medical examinations have become more comprehensive.

 In a Danish study, overall mortality was increased among seafarers compared to the population ashore, and mortality from cirrhosis of the liver was increased in deck and engine crew and in deck officers [4].

 In a British pathology study of 111 cases of primary hepatic malignancy collected in the Liverpool region [23], Cruickshank noted that “although the incidence in the region as a whole was not unusually high, most of the cases were found in the vicinity of two ports, and the relatively large number of seafarers may give an indefinite hint of some aetiological relationship between seafaring and the disease”.

 Increased risks for primary liver cancer were observed in Sweden for occupations with high consumption of alcohol and/or high prevalence of smoking, like seamen, waiters and cooks [5].

 Another Danish series showed that the standardized incident ratio (SIR) of all cancers combined was higher than expected in seafarers: Male Danish seafarers have a high overall relative risk of cancer that is related to all cancers associated with tobacco smoking and alcohol (including mouth, pharynx, esophagus, and pancreas cancer), and a borderline increased excess of colon cancer, while female Danish seafarers have an excess of rectum cancer [6].

 An analysis of 2.8 million cancers among 15 million people, aged 30-64, in Denmark, Finland, Iceland, Norway and Sweden showed that the occupations with the highest SIR for all cancers combined included waiters, workers producing beverage and tobacco, seamen and chimney sweeps [7]. It was noted that exposure to the known hepatic carcinogens, the Hepatitis B virus and aflatoxin, is rare in the Nordic countries, and a large proportion of the primary liver cancers can therefore be attributed to alcohol consumption. The highest risks of liver cancer were seen in occupational categories with easy access to alcohol at the work place or with cultural traditions of high alcohol consumption, such as waiters, cooks, beverage workers, journalists and seamen [7]. However, in a serological study of 523 volunteers during compulsory health control before embarkation from the port of Oslo, the prevalence of hepatitis B markers was 9.4% which was significantly higher than in the general Norwegian population. The prevalence increased with the number of years of occupation, and was associated with frequent casual sexual contacts in foreign countries [24]. The prevalence of antibodies against hepatitis A (HAV) was 36% in seamen born in 1945 and earlier and 5% in younger individuals, an age-dependent pattern which is essentially similar in the general Norwegian population [24]. The authors’ conclusion was that the incidence of viral hepatitis infections in the occupation was noticeably high, suggesting that vaccination of seamen in certain areas of trade should be considered.

 In a large Danish series, SIR for hepatitis A was 1.77 for male seafarers compared with the general population, and SIR for hepatitis B was 3.02, the main risk factors being intravenous drug use and casual sex aboard[25]. The authors recommended that merchant seamen should be vaccinated against hepatitis A according to general recommendations for travelers [26]; thus seamen from low-endemic areas who eat and drink ashore in endemic areas should be recommended vaccination. Prophylaxis against hepatitis B should primarily be directed against blood-borne and sexually transmitted diseases in general, as HIV infection also has been found among seamen. Vaccination against hepatitis B should be reserved for special categories of personnel, such as ship officers who perform medical treatment as part of their duties on board, and therefore have a well-established, but limited risk of blood-borne disease [27].

 In a study comprising 24,765 male offshore workers, a four-fold excess risk of esophageal adenocarcinoma was found in upstream operators, who are assumed to have the most extensive contact with different phases of crude oil. The authors noted that a major limitation of the study was the lack of data on other risk factors of esophageal adenocarcinoma, such as prevalence of gastro-esophageal reflux and the lifestyle factors body mass index, smoking and alcohol consumption [28].

 Occupational associations with gastric cancer were investigated in a multicenter case-control study in Italy [29], and the only significantly increased risk was observed for ‘men who ever worked as sailors, seamen and allied groups (OR=2.9). The risk increased slightly to 3.1 among those employed for 21+ years.’ This was consistent with an earlier study which indicated an increased gastric cancer risk among Icelandic seamen, which the authors speculated might be due to consumption of home-smoked foods [30]. Also British Columbia and Singapore fishermen are reported to have an increased gastric cancer mortality and incidence [31,32].

 In a review of diseases and accidents among European seafarers (663,290 diagnoses from a total of15 countries from 1976 to 1990), accidents took first place with 18.5%, but diseases of the digestive system were those occurring most often (14.8%), ‘exactly as 10 years previously’ [8]. Italian seafarers were affected most frequently (25.6%), followed by Germans (20.7%) and Greeks (18.7%). Gastritis and gastric and duodenal ulcers occurred as the most frequent disorders;  it was noted that seafarers suffer twice as often from digestive complaints as does the corresponding male population on land, and that a number of factors have a synergistic effect on chronic gastritis and gastric ulcers, like un-physiological rhythm during working time, monotony on board, seasickness, macro- and micro-climatic factors, excessive use/consumption of tobacco, alcohol and other stimulating beverages, stress and mental strain.

 In a gastroscopy study  from 1986, morbidity of peptic ulcer was found to be higher  in Chinese seafarers compared to controls [33], and in a Japanese analysis of 51,641 reported seafarer cases of accidents and disease that required more than 3 days off work, the most prevalent were diseases of the digestive system (33.5%); the proportions of  disorders in the digestive system varied from 21.4% in passenger vessels to 39.8% in specialized  ships, equally high for officers and ratings [34].

 In a report from Vietnam [35] there were more cases of diseases of the digestive system among 865 seafarers (12%) than in 881 controls (2%).

 In a Danish study of hospitalizations among seafarers on merchant ships [9], it was noted that despite pre-employment selection and biennial health examinations, a large proportion of the seafarers showed evidence of poor health. Hospitalizations because of diseases of the digestive system were second to only injuries. They were particularly high among ratings aboard passenger ships, a group dominated by catering crew and cooks. This may again reflect lifestyle factors including alcohol, active and passive smoking, and non-daytime work, and a similar hospitalization rate is found among people employed in the Danish hotel and restaurant industry [9,10].

 In another study of hospital contacts for chronic diseases among Danish seafarers and fishermen, high standardized hospital contact ratios were found, among others, for alcohol-related liver diseases in male officers[6].  

 Hansen et al. [9] also found a high ratio of seafarer hospitalizations in Denmark due to inguinal hernia and commented that this finding is likely to be iatrogenic: “The seafarers are checked for hernia at biennial mandatory health examinations, which have almost certainly caused many referrals for surgical repair of hernia”.