Nutritional intakes and associated factors among tuberculosis patients: a cross-sectional study in China

This cross-sectional study was undertaken as part of the project “Investigation of nutrition and diet of patients with pulmonary tuberculosis in poor areas in China” supported by the World Health Organization Regional Office in the Western Pacific. It was conducted from November 2015 to April 2017 in two counties, Lingyun county in Guangxi province and Lin county in Shanxi Province. These two counties were national impoverished counties, and did good job in TB management. TB case notification rates in 2016 were 106.97 per 100,000 and 63.16 per 100,000 in Lingyun county and Lin county, respectively.

We focused our study on adult patients (age ≥ 18 years) with active TB who were registered in Tuberculosis management information system from Nov 1st, 2015 through May11^th, 2017. Patients with extrapulmonary tuberculosis, and those aged 18 years and below or with severe complications were not eligible for the study. Pregnant or breast-feeding women, and those who declined to sign the consent form were also excluded.

As BMI is commonly used in nutrition assessment, we applied the prevalence of BMI < 18.5 which is also defined as malnutrition [14] in determining sample size. We assumed that the prevalence of malnutrition in the general population in poor areas and TB patients would be 6.7% [15] and 25.0% [2], respectively, and the required sample size was calculated to detect difference in the two proportions. The probability of a type I error was set at 0.05, the power of the study was estimated at 90% and the design effect was set at 1, determining a sample size of TB patients was 77 per study site. Considering participants’ refusal, we expanded the sample size to 150 per study site, and the final sample size of TB patients was 300 totally.

Data for associated factors were taken from a questionnaire, including socio-demographic attributes (age, gender, education level, marital status, occupation and household income level) and behavioral variables (alcohol consumption, smoking status and eating out-of-home).

In line with Chinese Dietary Reference Intakes (DRIs) 2013 [16], we categorized patients’ ages into 3 groups: 18–49 years, 50–64 years, 65 years and above to facilitate comparisons. Educational level was classified into primary school and below, junior middle school and above. Household income level was proxied as annual household income and was grouped into < ¥20,000, ¥20,000 - ¥40,000, and ≥ ¥40,000 [17]. Alcohol consumption was surveyed as drinking wine, beer and Chinese spirit now or ever. A smoker was defined as smoking now or smoking previously but have stopped smoking in the evaluation period. Eating out-of-home was defined as eating at least one meal away from one’s own home or their residents’ home during the survey [18]. Severity of TB was grouped into two categories based on chest x-ray. Specifically, if the lesion was confined to two lung fields then it was defined as mild. If the lesion covered more than two lung fields or there were cavities, it was defined as severe [19].

Trained staffs performed face-to-face interviews for each participant to obtain dietary intake data through a 2-day 24-h dietary recall (24hdr) questionnaire, which was adapted from the method of 3-day 24hdr [20]. Participants were instructed to record all food intake at home and away from home in the previous 2 days (one weekday and one weekend day). Consumptions of condiments were also recorded through a questionnaire. All questionnaires were completed after the patient registering in Tuberculosis management information system and before anti-tuberculosis treatment.

Total energy, four macronutrients and sixteen micronutrients were evaluated. Nutrient intakes of each patient were converted to calories, weight of protein and weight of micronutrients based on Chinese Food Composition Tables (CFCT) 2004 [21].

To evaluate whether the patients’ nutrients were sufficient, we compared mean daily nutrient intakes of TB patients to Recommended Nutrient Intakes (RNIs) and Adequate Intakes (AIs) by Chinese dietary reference intakes (DRIs) 2013. Recommended Nutrient Intakes is an estimate of the amount of a nutrient that meets the requirements of most people (97–98%) within a specific physiological group (sex, age, body size, physical activity, type of diet). Adequate Intakes means a recommended intake value based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of healthy people [16].

The study was carried out on the basis of China Health and Nutrition Survey (CHNS) 2015, from which the investigating method and tool were used in our study. All on-site investigations were carried out by the county-level CDC and interviewers were trained with a standard protocol. Data was checked for completeness and accuracy on the day of investigation and sampled by provincial CDC for verification later. All data was double-entered into a database specially designed for this project.

All TB patients registered from Nov 1st, 2015 to May 11th, 2017 in Lin county were included in our study, while less than 40% of notified TB patients in Lingyun county have participated in this study.

The majority (53.7%) of TB patients aged between 18 and 49, with the mean age being 45.5 years old (standard deviation (SD):18.7). More than half (68.7%) of them were males. Most TB patients were married, employed and didn’t attend junior middle school and above, with annual household income less than ¥20, 000. Only 39.7% of them consumed alcohol, while 46.7% of them were smokers (Table 1).

The average daily energy was1655.0 kcal (SD: 619.3 kcal) and 1360.3 kcal (SD: 552.1 kcal) for males and females, respectively, which were significantly lower than recommended daily energy intake by DRIs (i.e., 2250 kcal and 1800 kcal for males and females). The protein intake was 44.6 g (SD: 18.2 g) and 35.9 g (SD: 12.3 g) for male and female TB patients, respectively. The protein daily intakes for our surveyed TB patients was significantly lower than daily protein intakes that were recommended by DRIs, which were 65 g and 55 g for males and females, respectively (Table 2). Our results also indicated that the male patients were more likely subjected to malnutrition. For example, percentages of male patients that had daily intakes below RNI/AI were 87.4 and 90.8% for daily energy intakes and protein intakes, respectively. Percentages for male patients were 59.9 and 58.4% for daily energy and protein intakes, respectively. As for micronutrients, for male TB patients, the mean daily intakes of retinol, niacin, vitamin E, sodium, iron, Manganese, copper and Phosphorus were higher than RNI/AI, while calcium, i.e., 216.3 mg, intake was severely less than RNI/AI (800 mg) (Table 3). For the female patients, the mean daily intakes of vitamin E, copper and sodium were higher than RNI/AI. However, the intakes of riboflavin, potassium and calcium were severely inadequate.

Our univariate analyses suggested that employment status influenced energy intake, with lower energy consumption was found for the patients that were unemployed (Table 4). Furthermore, annual household income was another factor that affected daily energy intakes, for the patients whose annual salary was more than ¥40,000 tended to have enough energy intakes. In multivariate analysis (Table 5), after adjusting for other factors, unemployed participants were more likely to have low energy intake (OR: 3.542; 95%CI: 1.471, 8.530) (p < 0.01). Meanwhile, lower protein intake was associated with eating at home. The possibility of low protein intake for people eating out-of-home was much lower than those eating at home (OR: 0.328; 95% CI: 0.133, 0.809) (p < 0.05).

Our study initiated in examining factors associated with TB patients’ nutrient intake and was also the first study in China to compare nutrient intakes of TB patients with the latest Chinese Dietary Reference Intakes (DRIs) 2013. However, there are still some limitations in our study. Firstly, the 24hdr method has its own shortcomings. Reliance on the memory of participants and recall bias could result in an underestimation of nutrient intakes [38]. Secondly, considering that more times we interviewed, less cooperate would TB patients be because they may be worried about being discriminated against, so we took the 2-day 24hdrs method instead of the commonly used 3-day 24hdrs, but the reliability may decrease. A study conducted among African American youth showed that reliability estimates for 3-day 24hdrs ranged from 27 to 62%, while, for 2-day 24hdrs, it ranged from 19 to 52% [39]. And, when measuring the consumption of condiments, we didn’t take the household weighing method commonly used in nutrition survey. Thirdly, we hope to enroll all eligible TB patients in these two counties notified from Nov 1st, 2015 to May 11th, 2017. All notified TB patients in Lin county were included in our study, while TB patients enrolled in our study accounted for less than 40% of all notified TB patients in Lingyun county during that period. Moreover, we measured socioeconomic status of TB patients only by annual household income and this was not enough to capture the economic disparities. All of these may result in that our findings could not be generalized to all the local people.