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• A blue bird flying across the blue sky
  Wenbin Liang
  Published on: 27 April 2016
• Dust exposure and cardiovascular morbidity
  Bengt Sjögren
  Published on: 27 April 2016
• Re: Authors' reply
  Wenbin Liang
  Published on: 27 April 2016
• Authors' reply to: A blue bird flying across the blue sky
  Riitta-Sisko Koskela
  Published on: 27 April 2016

• Published on: 27 April 2016

  A blue bird flying across the blue sky

  • Wenbin Liang, taking master of public health

  Dear Editor

  Exposure period is as important as the dose of exposure

  Based on Figure 1 in the article[1], it could be inferred that the timing of dust exposure would be crucial when investigating whether “Dust exposure” would increase the risk of IHD among patients who already had Respiratory diseases: The dust exposure of most interest would be the exposure after the occurrence of the respiratory dise...

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  Dear Editor

  Exposure period is as important as the dose of exposure

  Based on Figure 1 in the article[1], it could be inferred that the timing of dust exposure would be crucial when investigating whether “Dust exposure” would increase the risk of IHD among patients who already had Respiratory diseases: The dust exposure of most interest would be the exposure after the occurrence of the respiratory diseases. However people who were already diagnosed with respiratory disease especially those in more serious conditions were more likely to be moved away from the cohorts, therefore a great part of dust exposure among people with chronic respiratory diseases were likely to happen before the diagnosis of the respiratory diseases, may appear to have minimum direct effect on IHD.

  Smoking: a rope

  Moreover smoking as a great risk factor for both respiratory disease and IHD, but this study only treat smoke habits as a categorical variable[1], it is far from enough, for example only among subjects who are current smokers, people who have higher dose of exposure on tobacco smoke are more likely to have both respiratory disease as well as IHD. However an analysis only include life long non-smokers may reduce the shadow of bias in the picture. Furthermore it is unrealistic to measure the effect of interaction between smoking and aspiratory disease on incidence of IHD based on the assessments of exposures in this study.

  Reference

  1. Koskela R-S, M.p., Sorsa J-A, Klockars M, Respiratory disease and cardiovascular morbidity. Occup. Environ, 2005. 62.

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  Conflict of Interest:
  None declared.

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• Published on: 27 April 2016

  Dust exposure and cardiovascular morbidity

  • Bengt Sjögren, MD, PhD
  • Other Contributors:
    • Carl-Göran Ohlson

  Dear Editor,

  We have read the study on respiratory disease and cardiovascular morbidity by Koskela and coworkers with great interest.[1] They found no obvious effect of direct dust exposure on ischaemic heart disease (IHD) among granite workers and workers in metal industry such as foundry workers and iron foundry workers in Finland. Furthermore, there was a weak association between dust exposure and chronic bronc...

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  Dear Editor,

  We have read the study on respiratory disease and cardiovascular morbidity by Koskela and coworkers with great interest.[1] They found no obvious effect of direct dust exposure on ischaemic heart disease (IHD) among granite workers and workers in metal industry such as foundry workers and iron foundry workers in Finland. Furthermore, there was a weak association between dust exposure and chronic bronchitis and pneumoconiosis, respectively, among granite workers. However, there was an association between chronic bronchitis and IHD among granite workers and iron foundry workers.

  We want to make one comment regarding a possible bias towards unity- effect by the inclusion of non-exposed workers.

  The study by Koskela et al. comprises six cohorts. Three of these cohorts consist of 1000 iron foundry workers, 1000 metal product workers and 1000 electrical workers, respectively. The subjects selected into the cohorts were 400 current and 400 former male workers with the longest duration of employment and a further 200 with the shortest duration of employment.

  A possible association between air pollutants and IHD may have a similar mechanism as the association between smoking and IHD. Smoking more than 25 cigarettes per day is estimated to double the risk of IHD compared with non-smokers. This risk decreases after quitting smoking and becomes closer to the risk of non-smokers.[2] Thus, former dust exposed workers followed for 16 years may ultimately have a risk similar to non-exposed workers. Consequently, the findings of the study by Koskela and coworkers may underestimate the relation between dust exposure and the occurrence of IHD. We certainly agree with our Finnish colleagues that efforts to prevent IHD should both include the prevention of respiratory diseases and the control of dust exposure.

  We do not have any competing interest regarding this letter.

  References:

  1. Koskela R-S, Mutanen P, Sorsa J-A, Klockars M. Respiratory disease and cardiovascular morbidity. Occup Environ Med 2005; 62: 650-655.

  2. Doll R, Peto R, Wheatley K, Gray R, Sutherland I. Mortality in relation to smoking: 40 years’ observations on male British doctors. BMJ 1994; 309: 901-911.

  Bengt Sjögren, MD, PhD
  Work Environment Toxicology
  Institute of Environmental Medicine
  Karolinska Institutet
  P.O. Box 210
  SE-171 77 Stockholm
  Sweden
  Tel: 46 8 524 822 29
  Fax: 46 8 31 41 24
  E-mail: Bengt.Sjogren@ki.se

  Carl-Göran Ohlson, MD, PhD
  Department of Occupational and Environmental Medicine
  Örebro University Hospital
  SE-701 85 Örebro
  Sweden
  Tel.: +46 19 6022468
  Fax.: +46 19 120404
  E-mail: carl-goran.ohlson@orebroll.se

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  Conflict of Interest:
  None declared.

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• Published on: 27 April 2016

  Re: Authors' reply

  • Wenbin Liang, taking master of public health

  Dear Editor,

  I thank the authors for they reply.

  I was not against figure 1. Instead, I was concerning the second scenario in figure 1: people who had respiratory diseases would have a higher rate of IHD if they kept exposure to dust—there might be an interaction between respiratory diseases and dust exposure after. In the discussion of the paper it states that “The direct independent effect of dust exposu...

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  Dear Editor,

  I thank the authors for they reply.

  I was not against figure 1. Instead, I was concerning the second scenario in figure 1: people who had respiratory diseases would have a higher rate of IHD if they kept exposure to dust—there might be an interaction between respiratory diseases and dust exposure after. In the discussion of the paper it states that “The direct independent effect of dust exposure on IHD and other CVDs was small”, but many people who had been diagnosis for respiratory diseases would be removed from the dust exposure job (I am sorry that I express it as “cohort” in the last letter). Thus most people who already had been diagnosed for respiratory disease, were not exposed to dust exposure after they had been diagnosed, even the “cumulative exposure to dust was considered until the diagnosis date of ischaemic heart disease (IHD)” .

  However as the reply showed that "the exposure data only including dust exposure after the diagnosis of a respiratory disease," had a small effect, my question is answered.

  I thank the authors so much to give more detail on the information on smoking. Eletter is a great way to reduce the information lost which is due to limited space in paper journals. Would it be appropriate to encourage authors to add more detail on journal websites?

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  Conflict of Interest:
  None declared.

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• Published on: 27 April 2016

  Authors' reply to: A blue bird flying across the blue sky

  • Riitta-Sisko Koskela, epidemiologist, PhD, LicSocSc
  • Other Contributors:
    • Pertti Mutanen, Juha-Antti Sorsa, Matti Klockars

  Dear Editor,

  We thank Mr. Wenbin Liang for comments on our paper.

  The first part of the comments concerned criticism on our Figure 1 and handling of exposure data. Our Figure 1 is a schematic drawing. It was aimed only to portray how the explanatory variables precede the response variables in our two-stage model. The purpose of our study was not to investigate does "dust exposure increase the risk of IHD a...

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  Dear Editor,

  We thank Mr. Wenbin Liang for comments on our paper.

  The first part of the comments concerned criticism on our Figure 1 and handling of exposure data. Our Figure 1 is a schematic drawing. It was aimed only to portray how the explanatory variables precede the response variables in our two-stage model. The purpose of our study was not to investigate does "dust exposure increase the risk of IHD among patients who already had respiratory diseases". Therefore, the figure was not intended to express that question. The aim of our study was concentrated on the intermediate role of the respiratory diseases in the association of dust exposure with IHD. To predict IHD with the two-stage model we first used respiratory diseases and dust exposure as explanatory variables. Second, we studied respiratory diseases as response variables. The respiratory disease and exposure variables were time dependent in the model predicting IHD just due to the importance of the timing.

  All the cohort members have been followed up until the end of the whole follow-up period. Although the workers had moved to other jobs, e.g., to those of lower dust exposure, they remained in our cohort. Lifelong occupational histories (including confounding exposures) were collected via questionnaires. In the model, cumulative exposure to dust was considered until the diagnosis date of ischaemic heart disease (IHD) regardless of the diagnosis date of any respiratory disease. In the model where respiratory diseases were predicted, exposure was considered only until the occurrence of each respiratory disease.

  Changing out of dusty jobs does not remove the effect of earlier dust exposure on IHD as well as on respiratory diseases, because both of these diseases have developed as disease processes and are continuously developing. The date of diagnosis is just one time point during the development. In addition, some of the workers with a respiratory disease had continued working in their dusty jobs.

  Workers with a respiratory disease may have an increased risk to get IHD due to an additional dust exposure after the respiratory disease diagnosis. However, it is important to remember that those workers who don't yet have a diagnosis but who are under the process to develop a respiratory disease may have the same increased risk. Thus, it is more reasonable to use the cumulative dust exposure up to the date of IHD diagnosis. Further, if we had analyzed the exposure data only including dust exposure after the diagnosis of a respiratory disease, the resulted effect of dust exposure on IHD would have been small.

  The most important reason for the observed small effect of dust exposure on IHD seemed to be homogeneity in the exposure variable. This has been thoroughly discussed in our article.

  The second part of the comments concerned smoking. It is well known that smoking is a great risk factor for both respiratory disease and IHD. The following data on smoking were collected via questionnaires: age when started to smoke and age when stopped, current smoking (amount of cigarettes per day), lifelong smoking (amount of cigarettes per day, smoking years). The comparison of the different smoking variables (tables and models) showed that the classified variable lifelong smoking was the most suitable for this material. Further, we have not reported any results on the effect of interaction between smoking and respiratory diseases on incidence of IHD. Of course we studied in the models interaction between smoking and dust exposure as well as interaction between smoking and different respiratory diseases but these interactions seemed to be non- significant.

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  Conflict of Interest:
  None declared.

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