Abstract
Objective
It is unknown whether the decreasing prevalence of H. pylori infections is associated with the increase in obesity and asthma and allergy. In this study, we assessed if obesity plays an intermediate role between H. pylori infections and allergy.
Design
A population-based, nested case-control study of 10,005 participants within the second Nord-Trøndelag Health Study (HUNT2), Norway, was performed in 1995–1997. The presence of H. pylori was tested by an enzyme immunoassay Pyloriset EIA-IgG, and weight, height, and waist circumference were measured. Body mass index (BMI) and waist circumference were used as measures of general and abdominal obesity, respectively. Self-reported asthma and allergic diseases were collected through questionnaires. The odds ratios of H. pylori relative to asthma and allergic diseases were estimated by logistic regression models stratified by waist circumference categories.
Results
H. pylori infection was present in 31%, ever asthma was reported in 10.4% and allergic rhinitis in 16.2%. The mean BMI was 26.4 kg/m2 and the mean waist circumference was 86.6 cm. H. pylori infection was neither associated with asthma nor allergic diseases. However, when stratified by waist circumference, H. pylori infection was associated with 30–40% reduced odds of asthma and 25% reduced odds of allergic diseases in individuals with abdominal obesity (waist circumference ≥86 cm in women and ≥96 cm in men).
Conclusion
H. pylori infection is associated with reduced risk of asthma and allergy in individuals with abdominal obesity, suggesting a possible causal pathway from reduced H. pylori infections through obesity to increased risk of asthma and allergy.
Keywords: Helicobacter pylori, Asthma, Allergy, Obesity, Abdominal obesity
Introduction
Infection with Helicobacter pylori (H. pylori) is common in humans and associated with socioeconomic status and living conditions in childhood.1 In developed countries, the prevalence of H. pylori infections has rapidly decreased in parallel to economic improvement over the past decades.2 This might be due to improved hygiene and sanitation, less salted food, and possibly increased use of antimicrobial agents.
Interestingly, as the prevalence of H. pylori has declined, there has been a rise in the prevalence of asthma and allergic diseases (e.g., hay fever and atopy) in developed countries.3, 4, 5 Tobacco smoking, air pollution, allergens, microbial infection, and obesity are among the potentially attributable exposures that may cause the increase of asthma and allergic diseases.6, 7 As an indigenous microbiota, the decrease of H. pylori has been postulated to play a role in this increase.8 There have been quite a few epidemiologic studies examining the association between H. pylori and asthma and allergic diseases. The results, however, are largely controversial.9
Parallel to the decrease in H. pylori infections, there has been a global increase of obesity during the past decades.10, 11 Obesity is associated with chronic inflammation which may be involved in the allergic response.12 A positive association between obesity and asthma and allergic diseases has been reported in many studies.13, 14 Moreover, lack of H. pylori infection has been associated with obesity in accumulating studies.15, 16 Thus, there could be an association between H. pylori, obesity, and asthma and allergic diseases, but so far this has not been studied. Whether lack of H. pylori infection leads to increased risk of asthma and allergic diseases and obesity, independent of each other, or the lack of H. pylori infection leads to increased obesity and then increased risk of allergic diseases, as a part of the same causal pathway, is unknown. In this large population-based Norwegian study, we examined the association between H. pylori infection, obesity, and asthma and allergic diseases.
Methods
Study design
In this nested case-control study, data from the second survey of the Nord-Trøndelag Health Study (HUNT2) was used.17 In HUNT2, performed in 1995–1997, all residents of Nord-Trøndelag County aged 20 years and older were invited to answer questionnaires and interviews, participate in clinical examinations, and contribute with biological material. Among 65,237 participants in HUNT2 (69.5% of invited), serum from 10,005 randomly selected individuals were tested for H. pylori.
Study outcome
Asthma and allergy
Asthma and allergy were assessed through self-reported questionnaires in HUNT2. Asthma was defined as present if the participants reported to have or have had asthma (ever), or if they reported to use or have used asthma medication (definition I). To avoid misclassification with chronic obstructive pulmonary disease (COPD) due to tobacco smoking, we also defined asthma as for definition I, but excluding participants that had smoked for more than 10 years (definition II). The participants also reported age of onset of asthma. Allergic rhinitis was defined as present if the participants reported to have hay fever or nasal allergy.
Main exposures
H. pylori
Serological status of H. pylori IgG antibodies was analysed using the commercially available enzyme immunoassay Pylorisert EIA-IgG (Orion Diagnostica, Espoo, Finland) at Levanger Hospital, Norway. Assay for detection of H. pylori was performed in 1998. The cut-off level used for a positive H. pylori IgG was ≥300 U.18
General obesity and abdominal obesity
Trained personnel at the screening stations objectively measured height, weight, and waist circumference during HUNT2. Body mass index (BMI) was calculated by dividing weight in kilograms by height in meters squared (kg/m2) for estimation of general obesity. According to the World Health Organization's definitions, obesity was defined as BMI ≥30 and abdominal obesity as waist circumference ≥86 cm in women and ≥96 cm in men.
Other factors
The following factors were selected a priori and included in the analyses: sex, age, tobacco smoking, alcohol drinking (monthly frequency of drinking), physical activity (reported hours of physical activity [light and hard] per week in the last year), highest completed education, and family history of asthma and allergy. Except from sex and age, all factors were assessed through self-reported questionnaires. Family history of asthma or allergic rhinitis was reported on first degree relatives (parents, siblings, and children).
Statistical analysis
Logistic regression was used to assess odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between H. pylori, obesity, and asthma and allergy. Separate analyses were performed stratified for waist circumference categories based on the sex-specific intervals: <75, ≥75 to <86, and ≥86 for women; and <88, ≥88 to <96, and ≥96 for men. The fully adjusted analyses were performed with age as a continuous variable, while the other variables were categorized. Tobacco smoking was categorized as never, occasional, and daily. Alcohol drinking was categorized as never, infrequent (once a week or less), and frequent (more than once a week). Physical activity was categorized as inactive (no activity or less than one hour light activity a week), moderately active (1–2 hours light activity or less than 1 hour hard activity a week), and highly active (at least 3 hours light activity or at least 1 hour hard activity a week). Completed education was categorized as primary school, high school, and college/university. In order to entangle the complex relations between H. pylori, obesity and asthma and allergies, we performed a mediation analysis to estimate the indirect effect of obesity relative to the total effect of H. pylori on the outcome of interest. The SAS 9.4 for Window was applied for data management, descriptive statistical analysis and logistic regression. All statistical analysis were two sides with significant level at 0.05.
Ethical approval
The study has ethical approval through the Regional Committee for Medical and Health Research Ethics, Central Norway (2012/1878). In HUNT, all participants gave written informed consent when participating, stating that their data could be used in future medical research.
Results
Characteristics
In the study population, the mean age was 50 years, 54% were women, and 31% were H. pylori positive (Table 1). The mean BMI was 26.4 kg/m2 (men:26.4; women; 26.3, respectively) and the mean waist circumference was 86.6 cm (men: 92.3; women: 81.6, respectively). Ever having had asthma was reported by 10.4% and after excluding those smoking >10 years, the figure was 5.7%. Hay fever or nasal allergies were reported by 15.1% and allergic rhinitis (including use of anti-allergy medication) were present in 16.2%. In total, 26.5% of the 10,005 participants had asthma or an allergic disease.
Table 1.
Total | Asthma |
Hay fever or nasal allergies | Allergic rhinitis | Asthma or allergic rhinitis | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Definition I | Definition II | |||||||||||
Total | N | % | N | % | N | % | N | % | N | % | N | % |
10005 | 100 | 1041 | 10.40 | 569 | 5.69 | 1507 | 15.06 | 1620 | 16.19 | 2655 | 26.54 | |
Sex | ||||||||||||
Women | 5414 | 54.11 | 576 | 55.33 | 334 | 58.70 | 882 | 58.53 | 951 | 58.70 | 1488 | 56.05 |
Men | 4591 | 45.89 | 465 | 44.67 | 235 | 41.30 | 625 | 41.47 | 669 | 41.30 | 1167 | 43.95 |
Age | ||||||||||||
Mean (SD) | 50.11 (16.78) | 50.11 (17.51) | 46.31 (18.81) | 46.30 (16.08) | 46.54 (16.11) | 49.03 (16.97) | ||||||
Median (IQR) | 48.80 (27.00) | 49.40 (29.30) | 44.00 (31.30) | 43.90 (23.70) | 44.30 (24.05) | 47.70 (27.20) | ||||||
<40 | 3166 | 31.64 | 339 | 32.56 | 251 | 44.11 | 610 | 40.48 | 642 | 39.63 | 925 | 34.84 |
40- | 2046 | 20.45 | 189 | 18.16 | 87 | 15.29 | 317 | 21.04 | 342 | 21.11 | 526 | 19.81 |
50- | 1796 | 17.95 | 165 | 15.85 | 74 | 13.01 | 242 | 16.06 | 270 | 16.67 | 439 | 16.53 |
≥60 | 2993 | 29.92 | 348 | 33.43 | 157 | 27.59 | 338 | 22.43 | 366 | 22.59 | 765 | 28.81 |
Missing | 4 | 0.04 | ||||||||||
H. pylori IgG | ||||||||||||
Negative | 6924 | 69.21 | 711 | 68.30 | 418 | 73.46 | 1125 | 74.65 | 1201 | 74.14 | 1854 | 30.17 |
Positive | 3081 | 30.79 | 330 | 31.70 | 151 | 26.54 | 382 | 25.35 | 419 | 25.86 | 801 | 69.83 |
Body mass index | ||||||||||||
Mean (SD) | 26.36 (4.06) | 27.19 (4.51) | 27.01 (4.40) | 26.32 (4.15) | 26.39 (4.15) | 26.76 (4.31) | ||||||
Median (IQR) | 25.80 (5.00) | 26.50 (6.00) | 26.45 (6.10) | 25.80 (5.10) | 25.90 (5.20) | 26.20 (5.40) | ||||||
<20 | 273 | 2.73 | 22 | 2.13 | 14 | 2.47 | 41 | 2.73 | 44 | 2.73 | 64 | 2.42 |
20- | 3666 | 36.64 | 313 | 30.24 | 177 | 31.27 | 560 | 37.31 | 594 | 36.80 | 887 | 33.57 |
25- | 4362 | 43.60 | 440 | 42.51 | 237 | 41.87 | 651 | 43.37 | 701 | 43.43 | 1149 | 43.49 |
≥30 | 1656 | 16.55 | 260 | 25.12 | 138 | 24.38 | 249 | 16.59 | 275 | 17.04 | 542 | 20.51 |
Missing | 48 | 0.48 | ||||||||||
Waist circumference (cm) | ||||||||||||
Mean (SD) | 86.56 (11.86) | 89.25 (12.95) | 87.71 (12.47) | 85.85 (12.10) | 86.00 (12.10) | 87.64 (12.56) | ||||||
Median (IQR) | 86.00 (16.00) | 89.00 (18.00) | 87.00 (18.00) | 85.00 (16.00) | 86.00 (16.00) | 87.00 (18.00) | ||||||
Women<75; Men<88 | 3095 | 30.93 | 253 | 24.56 | 156 | 27.76 | 474 | 31.83 | 499 | 31.17 | 739 | 28.14 |
75 ≤ Women <86; 88 ≤ Men<96 | 3493 | 34.91 | 315 | 30.58 | 180 | 32.03 | 535 | 35.93 | 575 | 35.92 | 885 | 33.70 |
Women≥86; Men≥96 | 3303 | 33.01 | 462 | 44.85 | 226 | 40.21 | 480 | 32.24 | 527 | 32.92 | 1002 | 38.16 |
Missing | 114 | 1.14 | ||||||||||
Tobacco smoking | ||||||||||||
No smoking | 4112 | 41.10 | 380 | 36.50 | 380 | 66.78 | 703 | 46.65 | 742 | 45.80 | 1048 | 39.47 |
Smoking occasionally | 3057 | 30.55 | 355 | 34.10 | 140 | 24.60 | 452 | 29.99 | 488 | 30.12 | 822 | 30.96 |
Smoking daily | 2831 | 28.30 | 306 | 29.39 | 49 | 8.61 | 352 | 23.36 | 390 | 24.07 | 785 | 29.57 |
Missing | 5 | 0.05 | ||||||||||
Alcohol drinking | ||||||||||||
Never | 2373 | 23.72 | 276 | 26.51 | 145 | 25.48 | 379 | 25.15 | 400 | 24.69 | 664 | 25.01 |
Infrequent | 4572 | 45.70 | 454 | 43.61 | 259 | 45.52 | 724 | 48.04 | 776 | 47.90 | 1211 | 45.61 |
Frequent | 1399 | 13.98 | 140 | 13.45 | 58 | 10.19 | 208 | 13.80 | 226 | 13.95 | 361 | 13.60 |
Missing | 1661 | 16.60 | ||||||||||
Physical activity | ||||||||||||
Inactive | 1709 | 17.08 | 195 | 18.73 | 83 | 14.59 | 224 | 14.86 | 249 | 15.37 | 464 | 17.48 |
Moderately active | 2954 | 29.53 | 299 | 28.72 | 165 | 29.00 | 503 | 33.38 | 533 | 32.90 | 822 | 30.96 |
Highly active | 4234 | 42.32 | 428 | 41.11 | 257 | 45.17 | 678 | 44.99 | 723 | 44.63 | 1111 | 41.85 |
Missing | 1108 | 11.07 | ||||||||||
Education | ||||||||||||
Primary school | 3241 | 32.39 | 363 | 34.87 | 158 | 27.77 | 417 | 27.67 | 450 | 27.78 | 859 | 32.35 |
High school | 3191 | 31.89 | 322 | 30.93 | 169 | 29.70 | 457 | 30.33 | 500 | 30.86 | 829 | 31.22 |
College/university | 3095 | 30.93 | 297 | 28.53 | 209 | 36.73 | 581 | 38.55 | 610 | 37.65 | 838 | 31.56 |
Missing | 478 | 4.78 | ||||||||||
Family history of asthma | ||||||||||||
No | 7963 | 79.59 | 636 | 61.10 | 299 | 52.55 | 599 | 39.75 | 1026 | 63.33 | 1805 | 67.98 |
Yes | 2038 | 20.37 | 405 | 38.90 | 270 | 47.45 | 908 | 60.25 | 594 | 36.67 | 850 | 32.02 |
Missing | 4 | 0.04 | ||||||||||
Family history of allergic rhinitis | ||||||||||||
No | 6927 | 69.24 | 577 | 55.43 | 347 | 60.98 | 945 | 62.71 | 670 | 41.36 | 1411 | 53.15 |
Yes | 3074 | 30.72 | 464 | 44.57 | 222 | 39.02 | 562 | 37.29 | 950 | 58.64 | 1244 | 46.85 |
Missing | 4 | 0.04 |
Asthma definition I: Asthma or medication for asthma.
Asthma definition II: Definition I, excluding those smoking for more than 10 years.
Allergic rhinitis: Hay fever or nasal allergies or use of anti-allergy medications.
SD: standard deviation.
IQR: interquartile range.
Associations
H. pylori infection was not associated with asthma or allergic diseases in general (Table 2), neither using the basic model, adjusting for sex and age, nor using the full model, also adjusting for BMI, tobacco smoking, alcohol drinking, physical activity, education, and family history of asthma and allergic diseases.
Table 2.
H. pylori infection |
||||
---|---|---|---|---|
Negative |
Positive |
dBasic model |
eFull model |
|
N | N | OR (95% CI) | OR (95% CI) | |
aAsthma (definition I) | 711 | 330 | 1.01 (0.87,1.17) | 1.00 (0.86,1.17) |
Asthma (onset at age<18) | 287 | 82 | 0.92 (0.70,1.20) | 0.93 (0.71,1.22) |
Asthma (onset at age≥18) | 228 | 141 | 1.07 (0.85,1.34) | 1.08 (0.85,1.36) |
bAsthma (definition II) | 418 | 151 | 0.90 (0.73,1.11) | 0.94 (0.76,1.16) |
Hay fever or nasal allergies | 1125 | 382 | 0.91 (0.79,1.04) | 0.93 (0.81,1.07) |
cAllergic rhinitis | 1201 | 419 | 0.93 (0.81,1.06) | 0.95 (0.83,1.09) |
Asthma or allergic rhinitis | 1854 | 801 | 1.02 (0.92,1.13) | 1.03 (0.92,1.14) |
Asthma definition I: Asthma or medication for asthma.
Asthma definition II: Definition I, excluding those smoking for more than 10 years.
Allergic rhinitis: Hay fever or nasal allergies or use of anti-allergy medications.
Basic model: Adjusted for sex and age.
Full model: Adjusted for sex, age, body mass index, tobacco smoking, alcohol drinking, physical activity, education, and family history of asthma or allergic rhinitis.
Effect modification analysis
However, when stratifying for waist circumference, H. pylori infection was associated with asthma and allergy in individuals with abdominal obesity (waist circumference ≥86 cm in women and ≥96 cm in men) (Table 3). In abdominal obesity, H. pylori infection was associated with a 40% reduced odds of asthma (definition I) with onset below 18 years of age (fully adjusted OR 0.61, 95% CI 0.37–0.99). H. pylori infection in abdominal obesity was not associated with asthma (definition I) with onset above 18 years of age (fully adjusted OR 0.98, 95% CI 0.71–1.35). Excluding those smoking for more than 10 years (definition II), H. pylori infection in abdominal obesity was associated with a 30% reduced odds of asthma (fully adjusted OR 0.70, 95% CI 0.50–0.97). H. pylori infection in abdominal obesity was also associated with a 25% reduced odds of hay fever or nasal allergies (fully adjusted OR 0.75, 95% CI 0.59–0.95).
Table 3.
Waist circumference (cm): women<75; men<88 |
Waist circumference (cm): 75 ≤ women<86; 88 ≤ men<96 |
Waist circumference (cm): women≥86; men≥96 |
||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
H. pylori infection |
H. pylori infection |
H. pylori infection |
||||||||||
Negative |
Positive |
Basic modeld |
Full Model |
Negative |
Positive |
Basic modeld |
Full Model |
Negative |
Positive |
Basic modeld |
Full Model |
|
N | N | OR (95%CI) | OR (95%CI) | N | N | OR (95%CI) | OR (95%CI) | N | N | OR (95%CI) | OR (95%CI) | |
Asthma (definition I)a | 193 | 60 | 0.97 (0.70,1.34) | 0.93 (0.67,1.30) | 213 | 102 | 1.16 (0.90,1.52) | 1.17 (0.89,1.53) | 297 | 165 | 0.91 (0.73,1.14) | 0.92 (0.73,1,15) |
Asthma (onset at age<18) | 102 | 24 | 0.97 (0.60,1.57) | 0.97 (0.59,1.59) | 87 | 31 | 1.19 (0.77,1.85) | 1.24 (0.77,1.94) | 90 | 24 | 0.58 (0.36,0.93)∗ | 0.61 (0.37,0.99)∗ |
Asthma (onset at age≥18) | 37 | 25 | 1.55 (0.89,2.70) | 1.46 (0.83,2.57) | 67 | 36 | 1.02 (0.66,1.57) | 1.00 (0.64,1.55) | 119 | 80 | 0.99 (0.73,1.35) | 0.98 (0.71,1.35) |
Asthma (definition II)b | 125 | 31 | 1.00 (0.65,1.54) | 1.05 (0.67,1.63) | 127 | 53 | 1.12 (0.79,1.59) | 1.23 (0.85,1.77) | 161 | 65 | 0.69 (0.50,0.94)∗ | 0.70 (0.50,0.97)∗ |
Hay fever or nasal allergies | 378 | 96 | 0.97 (0.75,1.27) | 0.98 (0.74,1.29) | 388 | 147 | 1.07 (0.86,1.33) | 1.09 (0.86,1.37) | 346 | 134 | 0.72 (0.57,0.91)∗ | 0.75 (0.59,0.95)∗ |
Allergic rhinitisc | 399 | 100 | 0.96 (0.74,1.25) | 0.97 (0.74,1.27) | 417 | 158 | 1.06 (0.85,1.31) | 1.07 (0.86,1.34) | 372 | 155 | 0.77 (0.62,0.96)∗ | 0.80 (0.64,1.01) |
Asthma or allergic rhinitis | 571 | 168 | 0.99 (0.80,1.223) | 0.99 (0.79,1.23) | 617 | 268 | 1.09 (0.91,1.30) | 1.10 (0.92,1.32) | 644 | 358 | 0.96 (0.81,1.13) | 0.98 (0.83, 1.16) |
Asthma definition I: Asthma or medication for asthma.
Asthma definition II: Definition I, excluding those smoking for more than 10 years.
Allergic rhinitis: Hay fever or nasal allergies or use of anti-allergy medications.
Basic model: Adjusted for sex and age.
p < 0.05.
Discussion
In the present study we found no association between H. pylori infection and asthma or allergic diseases in general. However, H. pylori infection was associated with a reduced risk of asthma and allergy in individuals with abdominal obesity, suggesting a possible causal pathway from reduced H. pylori infections through obesity to increased asthma and allergy.
The strengths of this study include the population-based design, large sample size, and random selection of participants where H. pylori status was assessed, reducing the risk of selection bias and chance findings. In addition, the HUNT study assessed a number of high quality variables that made adjustments for important confounders possible. The objective measurements of BMI and waist circumference are of great importance when assessing obesity. One weakness in this study is the self-reported asthma and allergy. This might introduce misclassification, mainly towards COPD. This is partly avoided by using a definition of asthma excluding participants that had smoked for more than 10 years (definition II) and stratified asthma with onset below 18 years of age (childhood asthma). Another weakness is the lack of data on cagA status, which has been regarded as an important factor in H. pylori infection that is negatively associated with asthma and allergy.19 As this is an observational study, causal associations cannot be claimed based on concurrent measurements of outcomes, exposures, and confounders.
A potential inverse relationship between H. pylori and asthma and allergy has been widely reported, although the results are controversial.20, 21, 22, 23, 24, 25 In the largest meta-analysis including 19 studies,9 an inverse association between H. pylori and asthma was demonstrated based on nine cross-sectional studies (pooled OR 0.84, 95% CI 0.74–0.96), but the pooled OR was not statistically significant in seven case-control studies (pooled OR 0.82, 95% CI 0.53–1.27) or three prospective cohort studies (pooled OR 0.82, 95% CI 0.53–1.27). Interestingly, the meta-analysis showed an inverse association in children (pooled OR 0.81, 95% CI 0.72–0.91) but not in adults (pooled OR 0.88, 95% CI 0.71–1.08), which is partially consistent with our results. The benefit of H. pylori in early life has been observed in quite a few studies,20, 21, 22, 26, 27 but at a late-in-life cost (e.g., H. pylori is a risk factor of peptic ulcer disease and stomach cancer).28 However, in the present study, such an inverse association were only identified in abdominally obese persons who had asthma or allergic rhinitis in their early life. This result may indicate an intriguing and complex relationship between H. pylori, obesity, and asthma and allergy.
A possible inverse relationship between exposure to H. pylori and the occurrence of obesity has been addressed as well,15, 29, 30, 31 although the results are still controversial.32 Moreover, whether H. pylori infection plays a role only in childhood or adult adiposity is unclear. As both H. pylori and obesity have been associated with asthma and allergic disease, the role of the two factors needs to be further clarified. Whether one factor is another factor's confounder, effect modifier or intermediate is unknown. In the present study, there was an association between H. pylori and asthma and allergic disease in abdominally obese participants, but this association disappeared in the non-abdominally obese population. This indicates that obesity may play a role as an effect modifier between H. pylori and asthma and allergy. As the analyses were based on cross-sectional data, potential obesity could be an intermediate in the pathway from H. pylori to asthma and allergy.
The underlying mechanisms between H. pylori, obesity, and asthma and allergy are plausible. H. pylori are one of the most common bacteria in humans, with prevalence rates of H. pylori in human populations ranging from 20 to 50%.33, 34 In the past decades, infection with H. pylori substantially declined due to improved living conditions and increased use of antibiotics. Individuals exposed to H. pylori in early childhood are prone to have a decreased appetite and food intake due to defective signalling of appetite- and satiety-related hormones in the stomach, e.g., ghrelin and leptin.20, 35 Hormone ghrelin exerts long-term appetite stimulating behaviour through its receptors in the hypothalamic paraventricular and arcuate nuclei.36, 37 Decreased exposure to H. pylori results in increased ghrelin and downregulated gastric leptin in children and in adults, thus increasing appetite stimulating behaviour and then leading to obesity. Interestingly, ghrelin has been associated with abdominal adiposity through regulation of lipid storage in abdominal white adipose tissue38; higher leptin levels has also been associated with abdominal obesity in quite a few studies.39, 40 In addition, H. pylori could be an indicator for changes in the gut microbiome. It reflects the complex interaction between microbes and the immune system.41, 42 When H. pylori are eradicated (other microbes will be influenced as well), the inner balance of microbes, appetite-related hormones, and the immune system will be broken, and then the person will become obese. The cytokines stimulated by chronic inflammation in the obese population will further trigger asthma and allergy. On the other hand, in obese persons, the cytokines may be supressed by infection with H. pylori. A protective association of H. pylori with asthma and allergic disease through obesity is plausible. This hypothesis aligns with the present study.
Another potential pathway is through Th1 and Th2 lymphocytes. A growing body of evidence indicates a preventive action of H. pylori to asthma and allergy probably through the gastric recruitment of regulatory T cells.43 It is well recognized that infections with H. pylori can trigger a Th1-mediated immune response.43 Activation of Th1 then suppresses the Th2 responses. The predominant activation of Th1 lymphocytes by H. pylori leads to the production of interferon gamma, interleukin 12, and tumor necrosis factor alpha in the stomach.44 Eradication of H. pylori will lead to inadequate Th1 response that might result in an overactive Th2 response with production of cytokines, including interleukins 4, 5, and 13, which are associated with the promotion of IgE and eosinophilic responses, and eventually allergies. The inverse association between H. pylori and asthma and allergic disease was first observed in 1989 with the “hygiene hypothesis”.45 It was based on observations of declining prevalence of allergic rhinitis with increasing number of older siblings. It suggested a preventive effect of transmitted infections in early childhood from older siblings. Exposure to infectious agents might educate the immune system and provide protection against allergic rhinitis. However, how obesity plays a role in this pathway is unclear. As the benefit of H. pylori was only shown in the obese population, the present study might suggest that the immune system educated by infection with H. pylori may be more alert to asthma and allergy in those obese.
In conclusion, this large population-based study found reduced risk of asthma and allergy with H. pylori infection in individuals with abdominal obesity. This suggests a possible protective effect of H. pylori infection in the development of asthma and allergy and possibly a causal pathway from reduced H. pylori infections through obesity to increased asthma and allergy.
Declarations
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
YXL proposed the conception of the study, designed the study based on the HUNT cohort, performed the data analysis and wrote the paper; ENJ designed the study, collected the data and participated in the analysis and wrote the paper; AL contributed specifically to the definition of asthma and allergic diseases using data from the HUNT cohort. He also contributed to the results interpretation and wrote the paper; KH designed the study, collected the data and contributed to results interpretation and manuscript writing. All authors of this paper have directly participated in the planning, execution, or analysis of the study, and have read and approved the final version submitted.
Authors' information
Not applicable.
Consent for publication
Not applicable.
Availability of data and materials
Results from the HUNTs have been published in numerous studies. Due to the current ethical issues, data was not supposed to be shared by the general public. Please contact the authors for data inquiry.
Funding
Not applicable.
Acknowledgement
The Nord-Trøndelag Health Study (The HUNT Study) is a collaboration between HUNT Research Centre (Faculty of Medicine, NTNU, Norwegian University of Science and Technology), Nord-Trøndelag County Council, Central Norway Health Authority, and the Norwegian Institute of Public Health.
Contributor Information
Eivind Ness-Jensen, Email: eivind.ness-jensen@ntnu.no.
Arnulf Langhammer, Email: arnulf.langhammer@ntnu.no.
Kristian Hveem, Email: Kristian.Hveem@ntnu.no.
Yunxia Lu, Email: yunxia.lu@uci.edu.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Results from the HUNTs have been published in numerous studies. Due to the current ethical issues, data was not supposed to be shared by the general public. Please contact the authors for data inquiry.