Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies

We combined data from 5 prospective studies to compare the death rates from common diseases of vegetarians with those of nonvegetarians with similar lifestyles. A summary of these results was reported previously; we report here more details of the findings. Data for 76172 men and women were available. Vegetarians were those who did not eat any meat or fish (n = 27808). Death rate ratios at ages 16-89 y were calculated by Poisson regression and all results were adjusted for age, sex, and smoking status. A random-effects model was used to calculate pooled estimates of effect for all studies combined. There were 8330 deaths after a mean of 10.6 y of follow-up. Mortality from ischemic heart disease was 24% lower in vegetarians than in nonvegetarians (death rate ratio: 0.76; 95% CI: 0.62, 0.94; P<0.01). The lower mortality from ischemic heart disease among vegetarians was greater at younger ages and was restricted to those who had followed their current diet for >5 y. Further categorization of diets showed that, in comparison with regular meat eaters, mortality from ischemic heart disease was 20% lower in occasional meat eaters, 34% lower in people who ate fish but not meat, 34% lower in lactoovovegetarians, and 26% lower in vegans. There were no significant differences between vegetarians and nonvegetarians in mortality from cerebrovascular disease, stomach cancer, colorectal cancer, lung cancer, breast cancer, prostate cancer, or all other causes combined.

Threats to applicability of randomised trials: exclusions and selective participation

BACKGROUND

Although the randomised controlled trial (RCT) is regarded as the 'gold standard' in terms of evaluating the effectiveness of interventions, it is susceptible to challenges to its external validity if those participating are unrepresentative of the reference population for whom the intervention in question is intended. In the past, reporting on numbers and types of potential subjects that have been excluded by design, and centres, clinicians or patients that have elected not to participate, has generally been poor, and the threat to inference posed by possible selection bias is unclear.

METHODS

A systematic review was undertaken, based largely on MEDLINE and EMBASE with follow-up of cited references, to assess the extent, nature and importance of excluding potential subjects or the unwillingness of particular centres, clinicians or patients to participate.

RESULTS

RCTs vary widely in the extent to which potential future recipients of treatment are included. The reasons cited for excluding certain categories of patient may be medical or scientific. Medical reasons include a high risk of adverse effects and the belief that benefit will be relatively small or absent (or has already been established) in the groups in question. Scientific reasons include more precise estimates of treatment effect because of a relatively homogeneous sample and the reduction of potential bias by excluding those individuals most likely to be lost to follow-up. Many RCTs have blanket exclusions, such as the elderly, women and ethnic minorities, but reasons for these exclusions are seldom given. Evaluative research is undertaken predominantly in university or teaching centres. Non-randomised studies are more likely than RCTs to include non-teaching centres. The effect of patient non-participation appears to depend on whether the RCT is concerned with treatment of an existing condition or with disease prevention. Participants in treatment trials tend to be more severely ill than those who do not participate. In contrast, those who participate in prevention trials are more likely to have adopted a healthy lifestyle than those who decline. Most evaluative studies fail to document adequately the characteristics of those who, while eligible, do not participate. However, subjects included in RCTs (i.e. eligible and participating) tend to have a different prognosis than patients identified from clinical databases.

CONCLUSIONS

Narrow inclusion criteria may offer benefits such as increased precision and reduced loss to follow-up, but there are important disadvantages, such as uncertainty about extrapolation of results, which may result in denial of effective treatment to groups who might benefit, and delay in obtaining definitive results because of reduced recruitment rate. Selective participation by teaching centres and sicker patients in treatment RCTs may exaggerate the measured treatment effect. Prevention trials, on the other hand, may underestimate effects as participants have less capacity to benefit.

An analysis of first-time enquirers to the CancerBACUP information service: variations with cancer site, demographic status and geographical location

A retrospective comparison of cancer incidence data and, where relevant, population data with 16,955 first-time users (patients, relatives and friends) of a national cancer information service (CancerBACUP) during the period April 1995 to March 1996 is presented. The number of events observed was compared with the number of events expected, were the national rates of cancer incidence and population demographics apply. Standardized incidence ratios (SIRs) (observed - expected ratios) were used to indicate any differences. Statistically significant differences (P < 0.001) in the observed and expected sex, age and primary site distribution of patients enquired about were found. Statistically significant differences (P < 0.001) were also identified for the age, employment status, socioeconomic class and geographical location of first-time enquirers (patients, relatives and friends). Enquiries about brain, testis and breast cancers and non-Hodgkin's lymphoma (NHL) were substantially higher than expected; enquiries about bladder, lung, stomach and colorectal cancers were much lower than expected. As the service is provided via a freephone number, it is available to all, and users might be expected to be randomly distributed across the variables listed. The underlying reasons for the differences identified need to be investigated, and the role of information in the care of cancer patients should be formally evaluated.

The role of carbohydrate reserves in the growth, resilience, and persistence of cabbage palm seedlings (Sabal palmetto)

Sabal palmetto (Walt.) Lodd. ex Schultes (cabbage palm) is an arborescent palm common in many plant communities throughout Florida, U.S.A., and the Caribbean. Although its seedlings grow very slowly in forest understories, they survive damage and defoliation well, and the species may increase in dominance following disturbances such as fire, logging, and hurricanes. We investigated the potential importance of total nonstructural carbohydrate (TNC) pools in the ability of cabbage palm seedlings to recover from the loss of aboveground tissue such as that caused by fire, grazing, or shallow burial by storm debris. TNC concentrations in belowground organs of seedlings from a forest understory were high, and TNC pools were sufficient to theoretically replace >50% of a seedling's canopy. The largest fraction of the belowground TNC pool was in stem tissue, where TNC in unclipped plants accounted for 26-54% of stem dry mass. Experimental reduction of TNC pools by repeated defoliation slowed seedling regrowth, and seedlings with inherently smaller pools (smaller seedlings) suffered higher mortality after repeated defoliation than did larger seedlings. Although regrowth and recovery after the loss of aboveground tissue was related to the size of the TNC pool in belowground organs, even the smallest seedlings with the smallest pools had sufficient stores to withstand at least two defoliations at frequent (7-week) intervals. Large belowground TNC pools in S. palmetto seedlings appear to enable them to survive all but the most frequent defoliations (e.g., frequent grazing or mowing). Allocation of resources to these stores, however, may contribute to the slow growth rates of S. palmetto seedlings in natural communities.

Mortality in vegetarians and non-vegetarians: a collaborative analysis of 8300 deaths among 76,000 men and women in five prospective studies

OBJECTIVE

To compare the mortality rates of vegetarians and non-vegetarians.

DESIGN

Collaborative analysis using original data from five prospective studies. Death rate ratios for vegetarians compared to non-vegetarians were calculated for ischaemic heart disease, cerebrovascular disease, cancers of the stomach, large bowel, lung, breast and prostate, and for all causes of death. All results were adjusted for age, sex and smoking. A random effects model was used to calculate pooled estimates of effect for all studies combined.

SETTING

USA, UK and Germany.

SUBJECTS

76,172 men and women aged 16-89 years at recruitment. Vegetarians were those who did not eat any meat or fish (n = 27,808). Non-vegetarians were from a similar background to the vegetarians within each study.

RESULTS

After a mean of 10.6 years of follow-up there were 8330 deaths before the age of 90 years, including 2264 deaths from ischaemic heart disease. In comparison with non-vegetarians, vegetarians had a 24% reduction in mortality from ischaemic heart disease (death rate ratio 0.76, 95% CI 0.62-0.94). The reduction in mortality among vegetarians varied significantly with age at death: rate ratios for vegetarians compared to non-vegetarians were 0.55 (95% CI 0.35-0.85), 0.69 (95% CI 0.53-0.90) and 0.92 (95% CI 0.73-1.16) for deaths from ischaemic heart disease at ages <65, 65-79 and 80-89 years, respectively. When the non-vegetarians were divided into regular meat eaters (who ate meat at least once a week) and semi-vegetarians (who ate fish only or ate meat less than once a week), the ischaemic heart disease death rate ratios compared to regular meat eaters were 0.78 (95% CI 0.68-0.89) in semi-vegetarians and 0.66 (95% CI 0.53-0.83) in vegetarians (test for trend P< 0.001). There were no significant differences between vegetarians and non-vegetarians in mortality from the other causes of death examined.

CONCLUSION

Vegetarians have a lower risk of dying from ischaemic heart disease than non-vegetarians.

Are randomized controlled trials controlled? Patient preferences and unblind trials

The most reliable information about treatment effects comes from randomized controlled trials (RCTs). However, the possibility of subtle interactions--for example, between treatment preferences and treatment effects--is generally subordinated in the quest for evidence about main treatment effects. If patient preferences can influence the effectiveness of treatments through poorly understood (psychological) pathways, then RCTs, particularly when unblinded, may wrongly attribute effects solely to a treatment's physiological/pharmacological properties. To interpret the RCT evidence base it is important to know whether any preference effects exist and, if so, by how much they affect outcome. Reliable measurement of these effects is difficult and will require new approaches to the conduct of trials. In view of the fanciful image with which such effects are portrayed and the uncertainties about their true nature and biological mechanisms, existing evidence is unlikely to provide sufficient justification for investment in trials. This is a Catch 22. Until an escape is found we might never know, even approximately, how much of modern medicine is attributable to psychological processes.

Postoperative artificial nutrition. Overuse or misuse?

The practice of postoperative artificial nutrition (PAN) in elective surgery was covered by a consensus conference in France (December 16,1994). Artificial nutrition was defined as the intake of at least two macronutrients (protein, lipid, and carbohydrate) through an artificial pathway (enteral/parenteral). The guidelines resulting from the conference (2) recommended prescribing artificial nutrition for only malnourished patients, patients with insufficient postoperative nutrient intake lasting 7 or more days, and patients with severe postoperative complications. These were similar to American guidelines produced in 1993 (1).

Technical complications of endovascular abdominal aortic aneurysm repair

PURPOSE

Results from 34 endovascular repairs of abdominal aortic aneurysms are reviewed to identify technical complications and relate them to anatomic and technical features of the operation.

METHODS

Twenty-one patients underwent attempted tube graft repair (mean follow-up, 13 months). Thirteen patients underwent placement of a bifurcated graft (mean follow-up, 7.2 months).

RESULTS

Twenty-five patients (74%) underwent repair without technical complication (16 tube graft and nine bifurcated graft). Of five patients who had tube graft complications, two involved small iliac arteries and resulted in arterial injury. One of these patients needed a femorofemoral bypass procedure, and the other required conversion to standard operation. Two patients had distal leaks associated with the attachment system, and one patient had misplacement of the distal attachment system. The two patients who had leaks were followed-up; one required operation after 7 months, whereas the other leak sealed. The patient who had distal attachment system misplacement had a second endograft placed within the first to provide a distal seal. The four patients who had bifurcated graft complications involved two graft limb stenoses, one managed with a Palmaz stent and the other with balloon angioplasty. The patient treated with balloon angioplasty had graft thrombosis 1 week after the operation, which resulted in the need for a femorofemoral bypass procedure. Another bifurcated graft patient had a graft limb twist, which has resulted in chronic claudication. One patient had placement of a limb too proximal in the common iliac artery with chronic leak, and an open operation was performed 18 months later.

CONCLUSIONS

Technical complications in this series seem to be associated with short distal necks, small iliac arteries, tortuous iliac arteries, and atherosclerosis at the aortic bifurcation. We believe that experience and understanding of these issues will reduce the risk of these complications in the future.

Why do women doctors in the UK take hormone replacement therapy?

STUDY OBJECTIVES

To ascertain the determinants and experiences of hormone replacement therapy (HRT) use by menopausal women doctors.

DESIGN

Postal questionnaire.

SETTING

UK.

PATIENTS

A randomized stratified sample of women doctors who obtained full registration between 1952 and 1976, taken from the current Principal List of the UK Medical Register.

MAIN OUTCOME MEASURES

Current and previous use of HRT; reasons for and against HRT use; menopausal status; hormonal contraceptive use; lifestyle patterns; family and personal history of disease.

MAIN RESULTS

While 73.2% of 471 users had started HRT for symptom relief, 60.9% cited prevention of osteoporosis and 32.7 prevention of cardiovascular disease. Altogether 18.7% had started for preventive purposes alone. Significant predisposing factors to starting HRT were the presence and severity of menopausal symptoms, surgical menopause, past use of hormonal contraception, and a family history of osteoporosis. HRT users were also more likely to use skimmed rather than full fat milk, to try to increase their intake of fruit, vegetables, and fibre, and to undertake vigorous physical activity at least once a week. They were less likely to have had breast cancer. Long duration users were more likely than short duration users to be past users of hormonal contraception and to be using HRT for prevention of osteoporosis as well as symptom relief; they were less likely to have experienced side effects.

CONCLUSIONS

The high usage of HRT by women doctors reflects the fact that many started HRT on their own initiative and with long term prevention in mind. The results may become generalisable to the wider population as information on the potential benefits of HRT is disseminated and understood. However, HRT users may differ slightly from non-users in health-related behaviour and a substantial minority may never take up HRT, at least until the benefit-risk ratio is more clearly established.

Impact of postmenopausal hormone therapy on cardiovascular events and cancer: pooled data from clinical trials

OBJECTIVE

To examine the incidence of cardiovascular diseases and cancer from published clinical trials that studied other outcomes of postmenopausal hormone therapy as some surveys have suggested that it may decrease the incidence of cardiovascular diseases and increase the incidence of hormone dependent cancers.

DESIGN

Trials that compared hormone therapy with placebo, no therapy, or vitamins and minerals in comparable groups of postmenopausal women and reported cardiovascular or cancer outcomes were searched from the literature.

SUBJECTS

22 trials with 4124 women were identified. In each group, the numbers of women with cardiovascular and cancer events were summed and divided by the numbers of women originally allocated to the groups.

RESULTS

Data on cardiovascular events and cancer were usually given incidentally, either as a reason for dropping out of a study or in a list of adverse effects. The calculated odds ratios for women taking hormones versus those not taking hormones was 1.39 (95% confidence interval 0.48 to 3.95) for cardiovascular events without pulmonary embolus and deep vein thrombosis and 1.64 (0.55 to 4.18) with them. It is unlikely that such results would have occurred if the true odds ratio were 0.7 or less. For cancers, the numbers of reported events were too low for a useful conclusion.

CONCLUSIONS

The results of these pooled data do not support the notion that postmenopausal hormone therapy prevents cardiovascular events.

Mortality among appropriately referred patients refused admission to intensive-care units

BACKGROUND

The provision of intensive care is a perplexing issue for clinicians and the public. Concerns about the apparent lack of beds and the appropriateness of the patients admitted are tempered by the high cost of providing this service. As part of a study commissioned by the UK Department of Health, we tested the hypothesis that there is excess mortality among patients who are refused admission to intensive-care units.

METHODS

All referrals to six intensive-care units with different numbers of beds were monitored during a 3-month period. Data on mortality 90 days after first referral were obtained from family physicians for all patients known to be alive at hospital discharge. We adjusted, where possible, for confounding, including for age, sex, appropriateness of referral, disease severity, surgery and emergency categories, and bed provision. We did multivariate analysis by multiple logistic regression to compare the adjusted 90-day mortality rates for patients who were refused admission and for those admitted.

FINDINGS

480 patients were admitted and 165 were refused admission. 90 days after referral there had been 178 (37%) deaths among the admitted group and 75 (46%) among the refused group. After multivariate adjustment, 113 patients appropriately referred for intensive care but refused admission to their first-choice intensive-care unit had a relative risk of death of 1.6 (95% CI 1.0-2.5), compared with the group of appropriately admitted cases with medium APACHE II scores for disease severity. Age, the assessed need for treatment or monitoring interventions, and emergency status also contributed to differences in mortality among all referrals. Bed provision did not contribute significantly to excess mortality.

INTERPRETATION

Although this study is observational and case-mix adjustment is incomplete, we found a higher rate of attributable mortality in patients who were refused intensive care, particularly for emergency cases. We question whether the provision of more beds alone would be a solution and conclude that there is an urgent need for more appropriate admission and discharge criteria.