Influence of Occupational Exposure on Hyperuricaemia in Steelworkers: A Nested Case-Control Study | BMC Public Health


Demographic study

Participants in this study were steel company workers who underwent occupational health examination at Hongci Hospital, Tangshan City, Hebei Province, China from March 2017 to September 2017. Inclusion criteria of the cohort: officially employed workers, at least one year of service. Cohort exclusion criteria: hyperuricaemia and refusal to participate in this cohort study. A total of 4,247 workers from the steel company were included in the cohort. A follow-up survey of a total of 3,706 steelworkers between March 2019 and September 2019 was carried out, with a missing data rate of 12.74%. Cohort workers with recent-onset hyperuricaemia in steel enterprises are considered as the case group. From this cohort population, each newcomer patient was matched with a worker from the steel company without hyperuricaemia as a control according to the principle of matched design (same sex and same age) to form a control group. A total of 641 case-control pairs were ultimately included as samples after those with incomplete information were excluded.

All participants read and signed the informed consent form. The subject has been approved by the Medical Ethics Committee of North China University of Technology (No. 15006).


An individual survey was conducted by uniformly trained interviewers with a questionnaire designed by the group of subjects. The content of the questionnaire included gender, age, household size, monthly household income, education level, marital status, smoking status, alcohol status, tea status, physical exercise, work type, work type change, shift work, shift type, shift work change, working hours change, daily working hours, monthly rest time and history personal medical. Participants were also asked about the frequency of food intake (0 days per week, 1-2 days per week, 3-6 days per week, and 7 days per week). The foods were divided into different groups: vegetables, fruits, meat, eggs, dairy products, soy products and seafood.

Physical examination

Participants took off their shoes when their height and weight were measured using the ultrasonic height and weight measuring device. Measurements were taken three times and averaged. Body mass index (BMI) was calculated based on the measurement. The participant was instructed not to drink tea, coffee, alcohol, or other beverages that could affect blood pressure results. The participant was asked to pause for five minutes before the blood pressure measurement and to take the measurement three times with an interval of at least three minutes.

Laboratory examination

Subjects were required to fast for 12 h. The morning fasting blood and urine were collected by the laboratory department of Tangshan Hongci Hospital by 9:00 a.m. the next day. Blood, urine and blood biochemistry were examined by medical specialists.

On-site hygienic survey

The on-site hygiene study focused on heat, dust and noise.

The temperature measurement tool is the Wet Bulb Black Globe Temperature Gauge (WBGT). According to the relevant standard [20], the temperature should be measured during the hottest season of the year. The temperatures were measured at different workstations taking into account the specific conditions of the steel production unit. Three to six measurement points were selected for each workplace and the test was repeated three times at each measurement point, with the average taken as the final result.

Dust was measured with a dust sampler. Sampling points were chosen in accordance with the applicable standard [21] and special conditions of the workshop. The sample collection time for each sampling point was 45 min and the dust collector flow rate was set at 40 L/min. The calculation formula is as follows:

$$begin{array}{c}C=frac{mathrm{m}2-mathrm{m}1}{mathrm{Q}times mathrm{t}}times 1000#end {array}$$


where: C- dust concentration, mg/m.3

m2 – the mass of the filter membrane after sampling, mg.

m1 – the mass of the filter membrane before sampling, mg.

Q—flow, L/min.

t—sample time, min.

Noise tests have been carried out in accordance with current standards [22, 23] and the specific circumstances of the workplace. When the noise distribution in the workshop was uneven, the noise was divided into different sound zones according to the sound level, and two test points were set up in each zone. When the distribution of noise in the workshop was relatively homogeneous (the difference in sound level is less than or equal to 3 dB(A)), three measurement points were set up. The average value was taken as the final result after the measurement. The calculation formula for the sound level measurement is as follows:

$${L}_{Aeq,T}=10text{lg(}frac{1}{T}{sum }_{i=1}^{n}{T}_{i}{10 }^{0.1{L}_{Aeq,{T}_{i}}})$$


where: ({L}_{Aeq, {T}_{i}})– equivalent sound level during the time period TI.

({L}_{Aeq, T})— equivalent sound level for a full day.

n—the total number of periods.

T—the length of each period.

JI– I period of time.

The measurement of the cumulative exposure (CEM) of the steelworkers is calculated on the basis of the results of the on-site hygiene survey, combined with the evolution of the work status and the duration of occupational exposure. The formula is:

$$mathrm{CEM}={mathrm{L}}_{1} {mathrm{T}}_{1}+ {mathrm{L}}_{2} {mathrm{T}}_ {2}points points +{mathrm{L}}_{mathrm{n}} {mathrm{T}}_{mathrm{n}}$$


where: Lnot is the average exposure to the target harmful factor over a period of time Tnot.

Definition and grouping of indicators

Those with a blood uric acid value greater than or equal to 7.0 mg/dL in males and 6.0 mg/dL in females, as well as previous or ongoing treatment for gout, were diagnosed hyperuricaemia [24]. Non-smokers were defined as those who had never smoked from birth at the time of the survey. Former smokers were defined as those who had ever smoked but had quit for 6 months or more as of the date of this survey. People who had smoked at least 1 cigarette a day for six months or more at the time of the survey were defined as current smokers. People who drank alcohol more than twice a week, regardless of type of alcohol, and who had been drinking for more than a year were considered to be drinking. Food consumption frequency was divided into four categories: never (0 days per week), occasionally (1-2 days per week), frequently (3-6 days per week), and daily (7 days per week). In this study, the International Physical Activity Questionnaire (IPAQ) was used to analyze the physical activities of steelworkers [25]. Physical activities were categorized into light, moderate, and vigorous activities based on intensity, frequency, and overall weekly physical activity level. Shift work is a system of irregular working hours in which one or more teams perform tasks continuously for 24 hours by working in shifts without stopping. [26]. The cumulative number of night work days represents the total number of night work days performed by workers in the steel plant on the date of the survey. According to the relevant standard [20], work with a productive heat source and WBGT ≥ 25°C was defined as work exposed to heat. Dust exposure was defined based on the type of work, the work environment and the results of the site hygiene survey. [21]. Noise exposure was defined as workers who have been exposed to a noisy environment where the equivalent A-weighted sound pressure level of 8 hrs/d or 40 hrs/week is ≥ 80 dB, which may be harmful to health and hearing. [27].

Statistical methods

Continuous variables were described by means and standard deviations, and differences between groups were obtained by Student’s t test. Categorical variables were expressed by the number of individuals (%), and χ2 tests were used for comparisons between groups. Multifactorial analyzes were performed and multiplicative interactions between occupational risk factors were explored using conditional logistic regression models. Additive interactions were assessed using the attributable proportion of interaction (AP), excess relative risk of interaction (RERI), and synergy index (SI), calculated using from the Excel spreadsheet of Andersson et al. [28]. PA is the proportion of the risk due to the interaction in the doubly exposed group. When RERI is positive, it indicates an increased risk due to the additive interaction. The SI can be interpreted as the ratio of an increased risk due to the two exposures to the sum of the individual increased risks.

All statistical analyzes were performed using IBM SPSS 24.0 and Excel 2019. P


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