Altered salivary profile in heavy smokers and its possible connection to oral cancer

Saliva is the first biological fluid to encounter inhaled cigarette smoke, whose numerous carcinogens and oxidants are responsible for the oral cancer so prevalent among smokers. Whole saliva, collected from 25 consenting heavy smokers and from a control group of 25 age- and gender-matched non-smokers, was subjected to sialochemical, biochemical, immunological and oxidative analyses. The mean flow rate was significantly higher in smokers than in non-smokers, as were the median activity value of superoxide dismutase (SOD) and the total salivary antioxidant capacity (ImAnOx) (by 32% and 12%, respectively, p=0.05). The salivary carbonyl concentration (an oxidative stress indicator) was significantly higher by 126% (p=0.0006) among smokers, while lactate dehydrogenase, albumin, total immunoglobulin G, and the metalloproteinases MMP-2 and MMP-9 concentrations were significantly lower in the smokers, by 86% (p=0.003), 65% (p=0.003), 61% (p=0.048), 35% (p=0.005) and 55% (p=0.035), respectively. Apparently, the oral cavity's salivary antioxidant system fails to cope with the severe attack of reactive oxygen species originating in cigarette smoke. Moreover, various other salivary functional and protective parameters also decreased among the smokers. Hence, further research aimed at examining the possibility of administration of agents as antioxidants or saliva substitutes to the oral cavity of smokers should be considered.     

Indexing serum and mucous biochemical parameters of endangered Chinese sturgeon Acipenser sinensis with implications for health assessment

The Chinese sturgeon (Acipenser sinensis) is a critically endangered aquatic fish. Health monitoring and welfare assessments are critical for the conservation of Chinese sturgeon. In this study, biochemical parameters of serum and skin mucus in Chinese sturgeon were examined to evaluate the potential biomarkers. Serum and mucous samples were obtained from Chinese sturgeon, and the levels of total protein (TP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), creatine kinase (CK), lactic acid (LD), acid phosphatase (ACP), lysozyme (LYZ), glucose (GLU), and cortisol were determined. The concentrations of ALT, AST, cortisol, and LYZ were significantly higher in the mucous group than those in the serum group (p < 0.05). In addition, the concentrations of ALP, ACP, LD, LDH, CK, and TP were significantly higher level in the serum group than those in the mucous group (p < 0.05). Moreover, the correlations between serum and mucous biochemical parameters were established. Statistical analysis showed a positive correlation between serum and skin mucous markers (ACP, cortisol, and LYZ). AST versus ALT in serum and mucus showed a significant positive correlation (p < 0.01). A significant positive correlation was found between cortisol and CK in mucus (p < 0.01). Moreover, LD versus LDH in serum showed a significant but weak positive correlation (p < 0.01). Principal component analysis revealed a complete separation between the serum and mucous groups, with the biomarkers that contributed the most being ALP, TP, ALT, and AST. This study provides baseline data and reference intervals for serum and mucous biochemical parameters in presumably healthy Chinese sturgeons. The current study has important implications for the development of conservation strategies and the conservation status of critically endangered species.     

Interaction Between Zinc, Cadmium, and Lead in Scalp Hair Samples of Pakistani and Irish Smokers Rheumatoid Arthritis Subjects in Relation to Controls

The incidence of rheumatoid arthritis (RA) has been associated with cigarette smoking. The aim of our study was to assess the trace essential and toxic metals, cadmium (Cd), lead (Pb), and zinc (Zn), in scalp hair samples of 32 Irish and 46 Pakistani smokers and non-smokers RA male patients with age range 42-56 years. For comparison purpose, the scalp hair samples of 27 Irish and 55 Pakistani non-RA male subjects of the same age group were collected. The concentrations of trace and toxic elements were measured by inductive coupled plasma atomic emission spectrophotometer and atomic absorption spectrophotometer prior to microwave-assisted acid digestion. The validity and accuracy of the methodology was checked using certified reference materials and using conventional wet acid digestion method on the same certified reference materials (CRMs). The recovery of all studied elements was found to be in the range of 97.5-99.7% of certified reference values of CRMs. The results of this study showed that the mean values of Cd and Pb were significantly higher in scalp hair samples of both smoker and non-smoker RA patients than in referents (P < 0.001), whereas the concentration of Zn was lower in the scalp hair samples of smokers and non-smokers rheumatoid arthritis patients. The deficiency of Zn and the high exposure of Cd and Pb as a result of cigarette smoking may be synergistic risk factors associated with rheumatoid arthritis.     

The accumulated evidence on lung cancer and environmental tobacco smoke.

OBJECTIVE: To estimate the risk of lung cancer in lifelong non-smokers exposed to environmental tobacco smoke. DESIGN: Analysis of 37 published epidemiological studies of the risk of lung cancer (4626 cases) in non-smokers who did and did not live with a smoker. The risk estimate was compared with that from linear extrapolation of the risk in smokers using seven studies of biochemical markers of tobacco smoke intake. MAIN OUTCOME MEASURE: Relative risk of lung cancer in lifelong non-smokers according to whether the spouse currently smoked or had never smoked. RESULTS: The excess risk of lung cancer was 24% (95% confidence interval 13% to 36%) in non-smokers who lived with a smoker (P < 0.001). Adjustment for the effects of bias (positive and negative) and dietary confounding had little overall effect; the adjusted excess risk was 26% (7% to 47%). The dose-response relation of the risk of lung cancer with both the number of cigarettes smoked by the spouse and the duration of exposure was significant. The excess risk derived by linear extrapolation from that in smokers was 19%, similar to the direct estimate of 26%. CONCLUSION: The epidemiological and biochemical evidence on exposure to environmental tobacco smoke, with the supporting evidence of tobacco specific carcinogens in the blood and urine of non-smokers exposed to environmental tobacco smoke, provides compelling confirmation that breathing other people''s tobacco smoke is a cause of lung cancer.     

Influence of substrate carbon on the metabolism of Clostridium thermohydrosulfuricum

The concentration of carbon sources has a significant influence on the growth, carbohydrate uptake and metabolite distribution in Clostridium thermohydrosulfuricum. The growing concentrations of glucose or starch increase the production of ethanol and lactate, the intracellular fructose-1,6-diphosphate (FDP) and the specific activity of lactate dehydrogenase (LDH), but decrease the ethanol/lactate ratio.     

Some macromolecular abnormalities developed by the interaction of malathion and permethrin and subsequent refeeding in Tribolium castaneum larvae

The effects of sublethal treatments of malathion and malathion + permethrin combinations on activities of acetylcholine esterase (ChE), carbohydrate-metabolizing enzymes (amylase; lactate dehydrogenase, LDH), protein-metabolizing enzymes (alanine and aspartate aminotransferase, ALAT, ASAT), as well as acid and basic phosphatases (AcP and AkP, respectively), and Kreb's cycle enzymes (isocitrate dehydrogenase, ICDH) were studied on sixth instar larvae of the red flour beetle, Tribolium castaneum. In addition, the levels of lipid, cholesterol, glucose, glycogen, proteins, free amino acids (FAA), urea, and nucleic acids (DNA and RNA) were determined. Malathion (400 ppm) increased the activity of LDH (53%), as well as the concentrations of FAA (31%) and urea (39%). Malathion treatments of 400 ppm decreased the glucose (20%) and glycogen (24%) content but did not affect other enzymes and biochemical components. Permethrin (200 ppm) and malathion (20 ppm) mixtures increased the activities of ChE (708%) and LDH (55%), and raised the concentrations of FAA (26%), urea (24%), glucose (23%), lipid (14%), cholesterol (21%), DNA (24%), and RNA (8%). The decrease in AcP activity and in glycogen concentration observed with malathion was sustained by permethrin in the mixture. Permethrin + malathion mixtures also depressed the levels of AkP (30%), ICDH (24%), and glycogen (36%). The intensity of effects commensurated with the dose and duration of insecticide exposure. Refeeding showed tendencies towards normalization of various biochemical parameters.     

高邮杂交鲫（鲫♀×白鲫）及其亲本血清生化组成的比较研究

本文对高邮杂交鲫（鲫♀×白鲫♂）及其亲本血清生化组成的定量分析。结果表明,在测定的血清总蛋白、白蛋白、胆固醇、尿素氮、葡萄糖、乳酸脱氢酶、ａ－羟丁酸脱氢酶、ａ－淀粉酶和谷草转氨酶等九个生化指标中,大部分指标高邮杂交鲫与母本无显著差异,而与父本则有极显著差异。这从代谢方面论证了高邮杂交鲫是一个偏向于母本的杂交种。     

Lactate regulates pyruvate uptake and metabolism in the preimplantation mouse embryo

This study was an investigation of the interaction of lactate on pyruvate and glucose metabolism in the early mouse embryo. Pyruvate uptake and metabolism by mouse embryos were significantly affected by increasing the lactate concentration in the culture medium. In contrast, glucose uptake was not affected by lactate in the culture medium. At the zygote stage, the percentage of pyruvate taken up and oxidized was significantly reduced in the presence of increasing lactate, while at the blastocyst stage, increasing the lactate concentration increased the percentage of pyruvate oxidized. Lactate oxidation was determined to be 3-fold higher (when lactate was present at 20 mM) at the blastocyst stage compared to the zygote. Analysis of the kinetics of lactate dehydrogenase (LDH) determined that while the V(max) of LDH was higher at the zygote stage, the K(m) of LDH was identical for both stages of development, confirming that the LDH isozyme was the same. Furthermore, the activity of LDH isolated from both stages was reduced by 40% in the presence of 20 mM lactate. The observed differences in lactate metabolism between the zygote and blastocyst must therefore be attributed to in situ regulation of LDH. Activity of isolated LDH was found to be affected by nicotinamide adenine dinucleotide(+) (NAD(+)) concentration. In the presence of increasing concentrations of lactate, zygotes exhibited an increase in autofluorescence consistent with a depletion of NAD(+) in the cytosol. No increase was observed for later-stage embryos. Therefore it is proposed that the differences in pyruvate and lactate metabolism at the different stages of development are due to differences in the in situ regulation of LDH by cytosolic redox potential.     

Sequential thoracentesis: minor change of zinc compared to other selected essential trace elements in the serum

This study first indicates that the serum trace element Zn tends to decrease in the course of sequential thoracenteses. Other selected essential elements such as copper (Cu), manganese (Mn), molybdenum (Mo), and cobalt (Co) do not reveal loss changes in their serum levels. Therefore, Zn should be monitored in patients who undergo repeated thoracentesis. To measure the magnitude of changes in serum trace elements and the clinical relevance of potential imbalances, concentrations of the essential elements are analyzed in 57 serum/effusion pairs obtained from 5 patients (4 male, 1 female; age 28–78 yr) who underwent repeated thoracenteses as a result of recurrent pleural effusion. All patients declined other therapeutic options such as chemical pleurodesis and /or chest tube placement. The total volumes of fluid removed ranged from 2.3 to 19.3 L and the frequency of thoracentesis ranged from 6 to 15 within a period of 102–174 days. Two patients had benign pleural disease and three had malignancies. Three patients suffered from pleural effusions resulting from exudates (total protein content >3.0 g/dL, LDH >200 U/L), and two resulting from transudates (total protein <3.0 g/dL, LDH <200 U/L). All trace elements were simultaneously determined by inductively coupled argon plasma-mass spectrometry. In addition, the concentrations of the following clinically relevant parameters were analyzed by standard methods: total protein, pH, leukocyte count, lactate dehydrogenase, and glucose.     

Novel Treatment for Lead Exposure in Children with Autism

The pathogenesis of some cardiovascular diseases (CVDs) has been altered with changes in the balance of certain trace and toxic elements. The aim of the present study was to assess the role of zinc (Zn) and cadmium (Cd) in smoker and nonsmoker male CVD patients (n?=?457) of two age groups (31–45) and (46–60). The both elements were determined in biological samples (scalp hair, blood, and urine) of CVD patients and healthy referents for comparison purpose. The concentrations of Zn and Cd were measured by atomic absorption spectrophotometer prior to microwave-assisted acid digestion. It was observed that the mean values of Cd were significantly higher in the biological samples of smokers CVD as compared to nonsmoker CVD patients, while the level of Zn was lower in both smoker and nonsmoker patients. The concentrations of Zn in whole blood and scalp hair samples were lower in CVD patients as compared to referents (p?>?0.001). Results showed significant changes of levels of Cd and Zn in blood and scalp hair samples of CVD patients when compared with healthy referents, while reverse in the case of urine samples. It was observed that low Zn levels were associated with both smoker and nonsmoker CVD patients, while increased cadmium accumulation was observed in smoker patients as compared to nonsmoker patients (p?>?0.025).     

Dehydrogenase activity of the pineal gland during the estrous cycle

An investigation of the relationship of succinic dehydrogenase (SDH) and lactate dehydrogenase (LDH) in the pineal gland of the adult female albino rats was carried out during seven definitive stages of the estrous cycle: Early Estrus (E1), Late Estrus (E2), Metestrus (ME), Early Diestrus (D1), Late Diestrus (D2), Preproestrus (PPE) and Proestrus (PE). Controlled housing conditions were maintained on 7:00 A.M. to 7:00 P.M. light-dark cycle. The animals were necropsied at precise times after the onset of estrus and subsequent stages of the cycle. Comparative histochemical and biochemical analysis revealed the following for SDH activity: E2 greater than E1 greater than D2 greater than D1 greater than PPE greater than PE greater than ME; and for LDH activity: PE greater than E2 greater than ME greater than D1 greater than PPE greater than E1 greater than D2. Interrelationships are postulated between pineal SDH, GOT, GPT, and estrogen concentrations in the rat.     

Damage to DNA in cervical epithelium related to smoking tobacco.

OBJECTIVE--To determine whether tobacco smoking causes increased DNA modification (adducts) in human cervical epithelium. DESIGN--Comparison of DNA adducts measured by the technique of postlabelling with phosphorus-32 in normal ectocervical epithelium of smokers and non-smokers. A questionnaire on smoking habit and a urinary cotinine assay were used to identify smokers and non-smokers. SETTING--Cytology unit in large teaching hospital. SUBJECTS--39 women (11 current smokers, seven former smokers, and 21 who had never smoked) undergoing gynaecological treatment (colposcopy or hysterectomy). Nineteen members of staff who did not smoke as controls. INTERVENTIONS--Biopsy of normal ectocervical epithelium. Urine sample. MAIN OUTCOME MEASURES--Measurement of DNA adducts in cervical epithelial tissue of smokers and non-smokers. Smoking habit derived from results of questionnaire and urinary cotinine:creatinine ratio. Proportion of adducts in women with abnormal and normal results of cervical smear test. RESULTS--DNA samples from smokers (identified from questionnaire) had significantly higher median proportions of DNA adducts that non-smokers (4.62 (95% confidence interval 4.04 to 7.74) v 3.47 (2.84 to 4.78) adducts/10(8) nucleotides; p = 0.048). Exclusion of women whose urinary cotinine:creatinine ratio did not confirm their self reported smoking habit (smoker or non-smoker) increased this difference (4.7 (3.85 to 8.08) v 3.52 (2.32 to 4.95) adducts/10(8) nucleotides; p = 0.03). Women who had abnormal results of cervical smear tests had significantly higher proportions of adducts than those with normal results (4.7 (3.90 to 8.13) v 3.47 (3.06 to 5.36) adducts/10(8) nucleotides; p = 0.03). CONCLUSIONS--Tobacco smoking by women leads to increased modification of DNA in cervical epithelium, suggesting biochemical evidence consistent with smoking as a cause of cervical cancer.     

Growth and metabolism of marine fish Chinook salmon embryo cells: response to lack of glucose and glutamine

A peculiar phenomenon, differing from the response of mammalian cells, occurred when Chinook salmon embryo (CHSE) cells were passaged in the medium lacking of both glucose and glutamine. To elucidate metabolic mechanism of CHSE cells, the metabolism parameters, key metabolic enzymes, and ATP levels were measured at different glucose and glutamine concentrations. In the glutamine-free culture, hexokinase activity kept constant, and lactate dehydrogenase (LDH) activity decreased. This indicated that lack of glutamine did not expedite glucose consumption but made it shift to lower lactate production and more efficient energy metabolism. The results coincided with the experimental results of unaltered specific glucose consumption rate and decreased yield coefficients of lactate to glucose. In the glucose-free culture, simultaneous increase of glutaminase activity and of specific ammonia production rate suggested an increased flux into the glutaminolysis pathway, and increases of both glutamate dehydrogenase activity and yield coefficient of ammonia to glutamine showed an increased flux into deamination pathway. However, when glucose and glutamine were both lacking, the specific consumption rates of most of amino acids increased markedly, together with decrease of LDH activity, indicating that pyruvate derived from amino acids, away from lactate production, remedied energy deficiency. When both glucose and glutamine were absent, intracellular ATP contents and the energy charge remained virtually unaltered.Revisions requested 16 December 2004; Revisions received 24 January 2005     

Biochemical composition of benign thyroid cyst fluid

Although the availability of thyroid cyst fluid is easy by fineneedle aspiration, less is known about the biochemical composition of thyroid cyst fluid. The authors have, therefore, determined the biochemical composition of 18 benign thyroid cyst fluid specimens. They found that the activities of aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and the concentrations of total protein, total bilirubin, and uric acid were highly increased in thyroid cyst fluid specimens when compared with normal human serum specimens. The concentrations of glucose, cholesterol, and triglycerides in cyst fluid were within normal serum limits. Selenium (Se) concentrations in most cyst fluids were low. Moreover, there was no correlation between Se and other biochemical parameters. Protein electrophoresis of cyst fluid specimens yielded high concentrations of α₁ and especially α₂ globulin fractions indicating an inflammation. The concentrations or activities of biochemical analytes were not significantly different in pure and mixed cysts. Those parameters were also not significantly different between cyst fluids of different colors. The gross appearance of the fluid and the presence of certain biochemical analytes were consistent with a hemorrhagic origin of most of the cyst fluid specimens. However, some biochemical markers indicate that autolysis or necrosis of thyroid tissue may also contribute the composition of thyroid cyst fluid. The reason for lower Se concentration in the thyroid cyst fluid may be the lower Se concentration in the Turkish population. These results also suggest that the fluid color or nature of cyst, e.g., pure or mixed cyst, is not a main determinant of biochemical composition of benign thyroid cyst fluid.     

Influence of corticosterone acetate on the spleen in intact and ovariectomized rats.

Increasing evidence of the interaction of glucocorticoids and ovarian steroids prompted the current study. Effects of exogenously administered corticosterone acetate (3.5 mg/100 g b.w/day for one week) were examined on splenic nucleic acids, protein, lactate, and on lactate dehydrogenase (LDH) specific activity and its isozymes in ovariectomized and ovary-intact Wistar rats (65-75 days old). Ovariectomy resulted in no significant change in the parameters studied except DNA which increased significantly. The administration of corticosterone to these rats did not produce any remarkable change in the ovariectomy caused increase in splenic DNA content. Nevertheless, it decreased the ratio of heart type subunits (H)/muscle type subunits (M) [H/M] of LDH isozymes. In the case of ovary-intact rats, corticosterone produced an increase in the concentration of splenic lactate but a decrease in the H/M ratio. Exogenously administered corticosterone exerts selective synergistic interaction with ovarian hormones on splenic lactate. The specific activity of LDH and the concentrations of RNA and protein remained unchanged during the interaction between ovarian hormones and corticosterone.     

Effects of lithium on thrombopoiesis in patients with low platelet cell counts following chemotherapy or radiotherapy

Therapy for neoplasma is limited by hematological side effects of tumor-destructive therapy and, in part, makes expensive supportive care necessary to overcome and treat leukopenia and thrombocytopenia and their consequences. Thrombocytopenia is a major clinical problem caused by chemotherapy and radiotherapy. An effective and very cost-effective option for treating moderate neutropenia is the administration of lithium carbonate. Lithium induces the release of colony-stimulating factors (CSF) and therefore stimulates proliferation of neutrophil granulocytes. Other cytokines, such as interleukin-1 (IL-1), IL-6, and tumor-necrosis factor-α (TNF-α), are also stimulated. Apart from granulocyte-macrophage-CSF (GM-CSF), there have as yet been no reports of lithium salts inducing early activating factors for the megakaryocytic lineage, such as IL-3, IL-11, stem cell factor and flt-3 ligand, or maturation factors, such as thrombopoietin (TPO). A statistically significant increase in the mean number of platelets for patients with cell counts below 150,000/μL on the commencement of treatment with lithium carbonate could be observed. Patient tolerability of lithium carbonate therapy is very good. Patients with persistent leukopenia and thrombocytopenia following chemotherapy or radiotherapy can be treated with this trace element very cost-effectively. Unfortunately this treatment has not gained acceptance in clinical oncology in the face of extremely cost-intensive treatment with recombinant GM-CSF, IL-11 or, potentially, thrombopoietin.     

Changes in biochemical properties of myocardial lactate dehydrogenase during exposure of rats to high altitude.

Exposure of normal rats to chronic natural hypoxia has shown the following effect upon catalytic properties of myocardial lactate dehydrogenase (LDH): significant increase of the two substrates pyruvate and lactate in tissue extracts; no changes in electrophoretic patterns of the enzyme; a slight enhancement of the activation energy of enzyme molecules; a significant increase in the Michaelis constant for pyruvate. Variations in biochemical properties of LDH appear after 12 ueeks of life in high altitude environment. These adjustments may be related to the stimulation of anaerobic metabolism induced by altitudinal hypoxia. Changes in LDH biochemical parameters seem adaptative.     

Oxygen and substrate deprivation on isolated rat cardiac myocytes: temporal relationship between electromechanical and biochemical consequences

The effects of hypoxia and reoxygenation on action potentials (AP), contractions, and certain biochemical parameters were studied in isolated rat ventricular myocytes in monolayer culture in the presence and absence of glucose. Substrate deprivation alone had no influence on the basal properties. In the presence of glucose, a 4-h hypoxic treatment caused only a moderate decrease in AP amplitude and rate. In substrate-free conditions, hypoxia induced a gradual decline in plateau potential level and in AP duration and rate, followed by rhythm abnormalities and a failure of the electromechanical coupling. Spontaneous AP generation then ceased, and the resting potential decreased with increased duration of hypoxia. These alterations were associated with a decrease in ATP content, an increase in the lactate production, and a leakage of about 50% of the total cellular lactate dehydrogenase (LDH). Cells reoxygenated after 150 min hypoxia recovered near-normal function, while the ATP depletion ceased and the rate of lactate and LDH loss was diminished. Conversely, cells reoxygenated after 4 h hypoxia exhibited a further decrease of the residual resting polarization and no change in the decline of intracellular ATP and in the efflux of cytosolic lactate and LDH. The results of this study indicate that (1) the sequence and the extent of functional alterations are dependent on the duration of hypoxia in the absence of exogenous substrate and (2) ATP depletion and the amount of lactate and LDH released during hypoxia are related to the shift from reversibly to irreversibly damaged cells.     

Androgen-responsive and nonresponsive prostate cancer cells present a distinct glycolytic metabolism profile

Prostate cancer (PCa) progresses from an early stage, confined to prostate, to a more aggressive metastasized cancer related with loss of androgen responsiveness. Although, it has been recognized that PCa cells have unique metabolic features, their glycolytic profile in androgen-dependent and androgen-independent stages of disease is much less known. Hence, the main purpose of this study was to compare glucose metabolism in androgen-responsive (LNCaP) and androgen-nonresponsive (PC3) PCa cells. Cell culture medium was collected and differences in glucose consumption and, lactate and alanine production were measured using Proton Nuclear Magnetic Resonance ((1)H NMR) spectra analysis. The mRNA and protein expression of glucose transporters (GLUT1 and GLUT3), phosphofructokinase 1 (PFK1), lactate dehydrogenase (LDH) and monocarboxylate transporter (MCT4) were determined by real-time PCR and Western Blot, respectively. The obtained results demonstrate that androgen-responsive (LNCaP) and androgen-nonresponsive (PC3) cells consumed similar amounts of glucose, whereas PC3 cells present higher lactate production. This increase in lactate production was concomitant with higher levels of MCT4 protein, increased LDH activity and higher lactate/alanine ratio, also suggesting increased levels of oxidative stress in PC3 cells. However, protein levels of LDH, associated with lactate metabolism, and GLUT3, involved in glucose uptake, were decreased in PC3 comparatively with LNCaP. Androgen-responsive and nonresponsive PCa cells present distinct glycolytic metabolism profiles, which suggest that targeting LDH and MCT4 metabolic pathways may be an important step for the development of new diagnostic and therapeutic strategies in the different stages of PCa.     

Does breathing other people's tobacco smoke cause lung cancer?

The available epidemiological studies of lung cancer and exposure to other people''s tobacco smoke, in which exposure was assessed by whether or not a person classified as a non-smoker lived with a smoker, were identified and the results combined. There were 10 case-control studies and three prospective studies. Overall, there was a highly significant 35% increase in the risk of lung cancer among non-smokers living with smokers compared with non-smokers living with non-smokers (relative risk 1.35, 95% confidence interval 1.19 to 1.54). Part of this increase was almost certainly caused by the misclassification of some smokers as non-smokers. As smokers, who are more likely to get lung cancer than non-smokers, tend to live with smokers this misclassification probably exaggerated the estimated increase in risk. Adjustment for this error reduced the estimate to 30% (relative risk 1.30), but as people who live with non-smokers may still be exposed to other people''s smoke this estimate was revised again to allow for the fact that a truly unexposed reference group was not used. The increase in risk among non-smokers living with smokers compared with a completely unexposed group was thus estimated as 53% (relative risk of 1.53). This analysis, and the fact that non-smokers breathe environmental tobacco smoke, which contains carcinogens, into their lungs and that the generally accepted view is that there is no safe threshold for the effect of carcinogens, leads to the conclusion that breathing other people''s tobacco smoke is a cause of lung cancer. About a third of the cases of lung cancer in non-smokers who live with smokers, and about a quarter of the cases in non-smokers in general, may be attributed to such exposure.