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In practice we do not always have clear guidance from economic theory about specifying an econometric model. At one extreme, it may be said that we should “let the data speak.” It is good to know that when they “speak” that what they say makes sense. We must be aware of a particularly important phenomenon in empirical econometrics: the spurious relationship. If you encounter a spurious relationship but do not recognize it as such, you may inadequately consider such a relationship for hypothesis testing or for the creation of forecasts. A spurious relationship appears when the model is not well specified. In this chapter, we see from a case study that people can draw strong but inappropriate conclusions if the econometric model is not well specified. We see that if you a priori hypothesize a structural break at a particular moment in time, and based on that very assumption analyze the data, then it is easy to draw inaccurate conclusions. As with influential observations, the lesson here is that one should first create an econometric model, and, given that model, investigate whether there could have been a structural break.
Dietary guidelines are increasingly promoting plant-based diets, limits on red meat consumption, and plant-based sources of protein for health and environmental reasons(1). It is unclear how the resulting food substitutions associate with insulin resistance, a risk factor for type 2 diabetes. Here, we modelled the replacement of red and processed meat with plant-based alternatives and the estimated effect on insulin sensitivity. We included 783 participants (55% female) from the Childhood Determinants of Adult Health (CDAH) study, a population-based cohort of Australians. In adulthood, diet was assessed at three time points using food frequency questionnaires: CDAH-1 (2004–06), CDAH-2 (2009–11), and CDAH-3 (2017–19). The median follow-up duration was 13 years. The cumulative average intake of each food group was calculated to reflect habitual consumption. Insulin sensitivity (%) was estimated from fasting glucose and insulin concentrations at CDAH-3 (aged 39–49 years) using homeostasis model assessment. Applying the partition model(2), we simulated the replacement of one food group with another by including both in the model simultaneously (e.g., red meat and legumes), along with potential confounders and energy intake. The difference between parameter estimates (i.e., regression coefficients and variances) and their covariance were used to estimate the “substitution” effect. We report the simulated percentage point change in log-transformed insulin sensitivity for a 1 serve/day lower intake of one food group with a 1 serve/day higher intake of another food group. Replacing red meat with a combination of plant-based alternatives was associated with higher insulin sensitivity (β = 0·10, 95% CI 0·04–0·16). Adjustment for waist circumference attenuated this association by 61·4%. On an individual basis, replacing red meat with legumes (β = 0·12, 95% CI 0·02–0·21), nuts and seeds (β = 0·15, 95% CI 0·06–0·23), or whole grains (β = 0·11, 95% CI 0·04–0·17) was likewise associated with higher insulin sensitivity. Point estimates were similar when replacing processed meat with plant-based alternatives, but more uncertain due to wide confidence intervals. Our modelling suggests that habitually replacing red meat, and possibly processed meat, with plant-based alternatives may associate with higher insulin sensitivity, and thus, a lower risk of type 2 diabetes. Abdominal adiposity was identified as a potentially important mediator in this relationship. In relation to insulin sensitivity, our findings support the recommendation to choose plant-based sources of protein at the expense of red meat consumption.
Although small fish are an important source of micronutrients, the relationship between their intake and mortality remains unclear. This study aimed to clarify the association between intake of small fish and all-cause and cause-specific mortality.
Design:
We used the data from a cohort study in Japan. The frequency of the intake of small fish was assessed using a validated FFQ. The hazard ratio (HR) and 95 % confidence interval (CI) for all-cause and cause-specific mortality according to the frequency of the intake of small fish by sex were estimated using a Cox proportional hazard model with adjustments for covariates.
Setting:
The Japan Multi-Institutional Collaborative Cohort Study.
Participants:
A total of 80 802 participants (34 555 males and 46 247 females), aged 35–69 years.
Results:
During a mean follow-up of 9·0 years, we identified 2482 deaths including 1495 cancer-related deaths. The intake of small fish was statistically significantly and inversely associated with the risk of all-cause and cancer mortality in females. The multivariable-adjusted HR (95 % CI) in females for all-cause mortality according to the intake were 0·68 (0·55, 0·85) for intakes 1–3 times/month, 0·72 (0·57, 0·90) for 1–2 times/week and 0·69 (0·54, 0·88) for ≥ 3 times/week, compared with the rare intake. The corresponding HR (95 % CI) in females for cancer mortality were 0·72 (0·54, 0·96), 0·71 (0·53, 0·96) and 0·64 (0·46, 0·89), respectively. No statistically significant association was observed in males.
Conclusions:
Intake of small fish may reduce the risk of all-cause and cancer mortality in Japanese females.
Edited by
David Kingdon, University of Southampton,Paul Rowlands, Derbyshire Healthcare NHS foundation Trust,George Stein, Emeritus of the Princess Royal University Hospital
This chapter gives an introduction to key concepts in epidemiology for the clinician, student, trainee or early career researcher interested in psychiatry and mental health. Following a brief introduction to the history of epidemiology, we provide a comprehensive, yet accessible introduction to key epidemiological concepts and how these apply to psychiatry and mental health. We introduce the major observational (cohort, case-control, cross-sectional, ecological) and experimental (randomised controlled trial) designs used in epidemiology, their strengths and limitations and specific issues for their use in psychiatry. We also cover measures of disease frequency (incidence, prevalence), measures of effect (risk, rate and odds ratios) and measures of impact (population attributable risk). Our chapter then provides a comprehensive introduction to traditional and contemporary approaches to understanding the critical issue of causation, illustrated via the use of causal diagrams known as Directed Acyclic Graphs. Throughout, we use accessible examples from published research and hypothetical worked examples to consolidate the reader’s knowledge about key methods in psychiatric epidemiology.
Soft drink consumption has become a highly controversial public health issue. Given the pattern of consumption in China, sugar-sweetened beverage is the main type of soft drink consumed. Due to containing high levels of fructose, a soft drink may have a deleterious effect on handgrip strength (HGS) due to oxidative stress, inflammation and insulin resistance. However, few studies show an association between soft drink consumption and HGS in adults. We aimed to investigate the association between soft drink consumption and longitudinal changes in HGS among a Chinese adult population. A longitudinal population-based cohort study (5-year follow-up, median: 3·66 years) was conducted in Tianjin, China. A total of 11 125 participants (56·7 % men) were enrolled. HGS was measured using a handheld digital dynamometer. Soft drink consumption (mainly sugar-containing carbonated beverages) was measured at baseline using a validated FFQ. ANCOVA was used to evaluate the association between soft drink consumption and annual change in HGS or weight-adjusted HGS. After adjusting for multiple confounding factors, the least square means (95 % CI) of annual change in HGS across soft drink consumption frequencies were −0·70 (–2·49, 1·09) for rarely drinks, −0·82 (–2·62, 0·97) for < 1 cup/week and −0·86 (–2·66, 0·93) for ≥ 1 cup/week (Pfor trend < 0·05). Likewise, a similar association was observed between soft drink consumption and annual change in weight-adjusted HGS. The results indicate that higher soft drink consumption was associated with faster HGS decline in Chinese adults.
Food insecurity (FI) is the lack of daily access for everyone to quality food in sufficient quantity. In many populations, it presents as a chronic and persistent condition. This study analysed the association between the length of time living with FI and socio-demographic conditions in households in a semi-arid municipality in the Brazilian Northeast between 2011 and 2019.
Design:
This is a population-based cohort study among families in the municipality in Northeast Brazil (2011, 2014 and 2019). FI was estimated through the Escala Brasileira de Insegurança Alimentar (EBIA, Brazilian Household Food Insecurity Measurement Scale), and the longitudinal category of time of living with FI was adopted to classify them according to the time they remained in FI during the cohort. The association with the socio-demographic profiles of the population was verified through multinomial logistic regression.
Setting:
Households in semi-arid, Northeast of Brazil.
Participants:
Household respondents interviewed in 2011, 2014 and 2019 (n 274).
Results:
Sixty-seven percentage (67 %) of families lived in FI in this period. Rural residence, low monthly per capita income and low schooling of the household reference person increased the chances of these families living longer in FI. These overlapping conditions increased the odds of FI in the household.
Conclusions:
Coping with FI requires intersectoral intervention that improves the socio-demographic conditions of the population.
Childhood infections have been shown to stunt growth, contribute to malnutrition and reduce cognition in early adulthood. This study aimed to assess relationships between early life infections and childhood cognition at age 11 years in the Newcastle Thousand Families Study (NTFS). The analysis included 741 members from the NTFS who had complete data for infections between birth and 5 years, and the 11-plus examinations. School records from the 11-plus examinations showed cognitive (IQ), English (EQ) and arithmetic (AQ) abilities. Housing conditions, overcrowding, birth order and social class were recorded at birth. Helicobacter pylori seropositivity was measured at age 49–51 years. Multivariable linear regression was used to examine relationships between infections and cognition. The total number of infections in the first 5 years of life was not significantly associated with IQ, EQ or AQ, nor were there significant relationships between cognitive outcomes and most infections. Tonsillitis did display a positive, significant association with IQ after adjustment for confounders (b = 6.43, 95% CI 0.92, 11.94, p = 0.022). Lower respiratory tract infections (LRTIs) showed significant negative relationships with all cognitive outcomes. H. pylori seropositivity at age 50 exhibited negative, significant relationships with EQ (p = 0.014) and AQ (p = 0.024) after adjustment for confounders. Although no significant relationship between overall infections and cognition were found, there were indications that LRTIs and gastrointestinal system infections may limit cognitive development. Given these infections remain prevalent, further research regarding severity and recurrence of infections and how they affect childhood cognition is needed.
Dietary guidelines are increasingly promoting mostly plant-based diets, limits on red meat consumption, and plant-based sources of protein for health and environmental reasons. It is unclear how the resulting food substitutions associate with insulin resistance, a risk factor for type 2 diabetes. We modelled the replacement of red and processed meat with plant-based alternatives and the estimated effect on insulin sensitivity. We included 783 participants (55 % female) from the Childhood Determinants of Adult Health study, a population-based cohort of Australians. In adulthood, diet was assessed at three time points using FFQ: 2004–2006, 2009–2011 and 2017–2019. We calculated the average daily intake of each food group in standard serves. Insulin sensitivity was estimated from fasting glucose and insulin concentrations in 2017–2019 (aged 39–49 years) using homoeostasis model assessment. Replacing red meat with a combination of plant-based alternatives was associated with higher insulin sensitivity (β = 10·5 percentage points, 95 % CI (4·1, 17·4)). Adjustment for waist circumference attenuated this association by 61·7 %. Replacing red meat with either legumes, nuts/seeds or wholegrains was likewise associated with higher insulin sensitivity. Point estimates were similar but less precise when replacing processed meat with plant-based alternatives. Our modelling suggests that regularly replacing red meat, and possibly processed meat, with plant-based alternatives may associate with higher insulin sensitivity. Further, abdominal adiposity may be an important mediator in this relationship. Our findings support advice to prioritise plant-based sources of protein at the expense of red meat consumption.
To assess the prospective association of two diet quality scores based on the Nova food classification with BMI gain.
Design:
The NutriNet-Brasil cohort is an ongoing web-based prospective study with continuous recruitment of participants aged ≥ 18 years since January 2020. A short 24-h dietary recall screener including ‘yes/no’ questions about the consumption of whole plant foods (WPF) and ultra-processed foods (UPF) was completed by participants at baseline. The Nova-WPF and the Nova-UPF scores were computed by adding up positive responses regarding the consumption of thirty-three varieties of WPF and twenty-three varieties of UPF, respectively. Participants reported their height at baseline and their weight at both baseline and after approximately 15 months of follow-up. A 15-month BMI (kg/m2) increase of ≥5 % was coded as BMI gain.
Setting:
Brazil.
Participants:
9551 participants from the NutriNet-Brasil cohort.
Results:
Increasing quintiles of the Nova-UPF score were linearly associated with higher risk of BMI gain (relative risk Q5/Q1 = 1·34; 95 % CI 1·15, 1·56), whereas increasing quintiles of the Nova-WPF score were linearly associated with lower risk (relative risk Q5/Q1 = 0·80; 95 % CI 0·69, 0·94). We identified a moderate inverse correlation between the two scores (–0·33) and a partial mediating effect of the alternative score: 15 % for the total effect of the Nova-UPF score and 25 % for the total effect of the Nova-WPF score.
Conclusions:
The Nova-UPF and Nova-WPF scores are independently associated with mid-term BMI gain further justifying their use in diet quality monitoring systems.
To evaluate the associations of ultra-processed food (UPF) consumption and obesity indicators among individuals with and without type 1 diabetes mellitus (T1DM) from the Coronary Artery Calcification in Type 1 Diabetes cohort study.
Design:
A secondary analysis. The consumption of UPF was assessed using the dietary data collected with the Harvard FFQ, and each food item was categorised according to the NOVA food processing classification. Height, weight and waist circumference were measured at baseline and after a mean of 14·6-year follow-up. Generalised estimating equations stratified by diabetes status were used to assess the associations between UPF intake and obesity indicators over 14 years of follow-up.
Setting:
USA.
Participants:
A total of 600 adults (256 T1DM and 344 non-diabetic controls) aged 39 ± 9·1 years at baseline and followed up for over 14 years were included.
Results:
Participants with T1DM consumed significantly more UPF than non-diabetic controls at baseline: 7·6 ± 3·8 v. 6·6 ± 3·4 servings per day of UPF, respectively (P < 0·01). Participants with T1DM and with the highest UPF intake had the highest weight (βQ4 v. Q1 = 3·07) and BMI (βQ4 v. Q1 = 1·02, all P < 0·05) compared with those with the lowest UPF intake. Similar positive associations were observed in non-diabetic controls.
Conclusions:
Individuals with T1DM may consume more UPF than non-diabetic controls. Positive associations between UPF consumption and obesity indicators suggest that limiting UPF can be recommended for obesity prevention and management. Further research is needed to confirm these findings.
Parents’ alcohol use is associated with alcohol use of their adolescent offspring, but does this association extend to the adulthood of the offspring? We examined associations of paternal and maternal problem drinking with lifetime problem drinking of their adult offspring prospectively assessed in a population-based Finnish twin-family cohort (FinnTwin16). Problem drinking (Malmö-modified Michigan Alcoholism Screening Test) was self-reported separately by mothers and fathers when their children were 16. The children reported on an extended lifetime version of the same measure during their mid-twenties (21-28 years) and mid-thirties (31-37 years). 1235 sons and 1461 daughters in mid-twenties and 991 sons and 1278 daughters in mid-thirties had complete data. Correlations between fathers’ and their adult children’s problem drinking ranged from .12 to .18. For mothers and their adult children, these correlations ranged from .09 to .14. In multivariate models, adjustment for potential confounders had little effect on the observed associations. In this study, parental problem drinking was modestly associated with lifetime problem drinking of their adult children. This association could be detected even when the children had reached the fourth decade of life.
Rapid prenatal and postnatal weight gain seem to alter appetite regulation and hypothalamic functions through different pathways; however, little is known on how early life growth trajectories may influence appetitive traits in school-age. We aimed to explore the associations between weight trajectories from birth to 5 years and appetitive traits at 7. Participants were from the Generation XXI birth cohort (n 3855). Four weight trajectories were investigated: ‘normal weight gain’ (closely overlaps the 50th percentile in the weight-for-age curve), ‘weight gain during infancy’ (low birth weight and weight gain mainly during infancy), ‘weight gain during childhood’ (continuous weight gain since birth) and ‘persistent weight gain’ (always showing higher weight than the average). Appetitive traits were assessed through the Children’s Eating Behaviour Questionnaire. Associations were tested using generalised linear models, adjusted for maternal and child characteristics. Compared with ‘normal weight gain’, those in the other growth trajectories showed greater enjoyment of food and eating in response to food stimuli (i.e. Food Responsiveness) but were less able to compensate for prior food intake and ate faster at 7 (i.e. less Satiety Responsiveness and Slowness in Eating). Also, those with ‘weight gain during infancy’ showed to have greater Emotional Overeating and less Emotional Undereating and were fussier. Associations were stronger if greater weight gain occurred during infancy. Early infancy seems to be a sensitive period in the development of later appetitive traits. The control of rapid growth during infancy, besides strategies focused on the overall environment where children are living, is necessary.
Increasing rates of caesarean sections has led to concerns about long-term effects on the offspring’s health, and it has been hypothesised that caesarean section induced differences in the child’s microbiota could potentially increase the risk of mental disorders.
Methods:
Nationwide Danish cohort study of 2,196,687 births was conducted between 1980 and 2015, with 38.5 million observation-years. Exposure was ‘Caesarean Section’ and outcome was the child’s risk of any mental disorder. Absolute and relative risks (RRs) were estimated using inverse probability weighting to adjust for age, calendar time and confounding variables while accounting for the competing risk of death.
Results:
Caesarean section (n = 364,908, 16.6%), compared to vaginal birth, was associated with a small RR increase of 8% (RR, 1.08; 95% CI, 1.04–1.13; n = 44,352) for the development of any in-patient psychiatric admission at age 36 for the offspring and with a small absolute risk difference of 0.47% (95% CI, 0.23–0.76). When looking at all in-patient, out-patient and emergency room psychiatric contacts among people born after 1995, the effect was diminished (RR, 1.04; 95% CI, 0.99–1.09; n = 15,211). The risk was comparable when comparing prelabour versus intrapartum caesarean section (RR, 0.98; 95% CI, 0.90–1.08) and acute versus planned caesarean section (RR, 1.00; 95% CI, 0.80–1.29).
Conclusion:
Birth by caesarean section was associated with only a very slightly increased risk of any in-patient psychiatric admission for the offspring and diminished even further when including all psychiatric contacts. The very small associations observed may be explained by unmeasured confounding and is unlikely to be of substantial clinical relevance.
The objectives of this study were (1) to systematically review the literature on the association between birth weight in children born in the first and second generation and (2) to quantify this association by performing a meta-analysis. A systematic review was carried out in six databases (PubMed, Science Direct, Web of Science, Embase, Scopus, CINAHL and LILACS), in January 2021, for studies that recorded the birth weight of parents and children. A meta-analysis using random effects to obtain a pooled effect of the difference in birth weight and the association of low birth weight (LBW) between generations was performed. Furthermore, univariable meta-regression was conducted to assess heterogeneity. Egger’s tests were used to possible publication biases. Of the 9878 identified studies, seventy were read in full and twenty were included in the meta-analysis (ten prospective cohorts and ten retrospective cohorts), fourteen studies for difference in means and eleven studies for the association of LBW between generations (twenty-three estimates). Across all studies, there was no statistically significant mean difference (MD) birth weight between first and second generation (MD 19·26, 95 % CI 28·85, 67·36; P = 0·43). Overall, children of LBW parents were 69 % more likely to have LBW (pooled effect size 1·69, 95 % CI (1·46, 1·95); I2:85·8 %). No source of heterogeneity was identified among the studies and no publication bias. The average birth weight of parents does not influence the average birth weight of children; however, the proportion of LBW among the parents seems to affect the offspring’s birth weight.
The current study aims to describe the consumption of ultra-processed foods, from 2 to 4 years old, and evaluate its association with growth outcomes during the same period. It is a prospective cohort study using data from the 2015 Pelotas-Brazil Birth Cohort. Outcomes assessed at the 2- and 4-year-old follow-ups were BMI-for-age Z-score and length/height-for-age Z-score. The exposure was a score of ultra-processed food consumption calculated at each follow-up by summing up the positive answers for the consumption of nine specific items/subgroups of ultra-processed foods: (i) instant noodles; (ii) soft drink; (iii) chocolate powder in milk; (iv) nuggets, hamburger or sausages; (v) packaged salty snacks; (vi) candies, lollipops, chewing gum, chocolate or jelly; (vii) sandwich cookie or sweet biscuit; (viii) juice in can or box or prepared from a powdered mix and (ix) yogurt. Crude and adjusted analyses between the score of ultra-processed foods and the outcomes were run using generalised estimating equations. Prevalence of consumption of ultra-processed foods increased from 2 to 4 years old, for all evaluated items/subgroups, except yogurt. In prospective analyses, higher scores of ultra-processed food consumption were associated with higher BMI-for-age Z-score and lower length/height-for-age Z-score, after adjustment for confounders. Ultra-processed food consumption, measured using a short questionnaire with low research burden, increased from 2 to 4 years old and was related to deleterious growth outcomes in early childhood. These results reinforce the importance of avoiding the consumption of these products in childhood to prevent the double burden of malnutrition and non-communicable chronic diseases throughout the life.
Edited by
James Law, University of Newcastle upon Tyne,Sheena Reilly, Griffith University, Queensland,Cristina McKean, University of Newcastle upon Tyne
Communication is both an activity in which we participate and the means by which we participate in a range of other activities. Therefore, the ability to communicate (or ‘communication capacity’) is closely linked with the ability to participate in life activities and in society. Cohort studies that consider communication capacity and explore participation in life activities provide an opportunity to understand these links at a single point in time or longitudinally. This chapter introduces the reader to four Australian cohort studies: Longitudinal Study of Australian Children (LSAC), Longitudinal Study of Indigenous Children (LSIC), Building a New Life in Australia: The Longitudinal Study of Humanitarian Migrants (BNLA), and the Australian Census of Population and Housing. The WHO's International Classification of Functioning, Disability and Health (ICF) is used as a framework to examine links between communication and participation. The chapter presents communication and participation data from the four cohort studies for children and adults who have speech, language and communication needs (SLCN), as well as people who are Indigenous (First Nations), multilingual and migrants, to reflect strengths and capacity within communities and societies.
Optimizing research on the developmental origins of health and disease (DOHaD) involves implementing initiatives maximizing the use of the available cohort study data; achieving sufficient statistical power to support subgroup analysis; and using participant data presenting adequate follow-up and exposure heterogeneity. It also involves being able to undertake comparison, cross-validation, or replication across data sets. To answer these requirements, cohort study data need to be findable, accessible, interoperable, and reusable (FAIR), and more particularly, it often needs to be harmonized. Harmonization is required to achieve or improve comparability of the putatively equivalent measures collected by different studies on different individuals. Although the characteristics of the research initiatives generating and using harmonized data vary extensively, all are confronted by similar issues. Having to collate, understand, process, host, and co-analyze data from individual cohort studies is particularly challenging. The scientific success and timely management of projects can be facilitated by an ensemble of factors. The current document provides an overview of the ‘life course’ of research projects requiring harmonization of existing data and highlights key elements to be considered from the inception to the end of the project.
Adult children with siblings can share caring for older parents but adult only children face this responsibility alone. Given increased longevity and reliance on informal care-giving, as well as an increase in one-child families, there is a need to investigate only children's care-giving further. Using data from three large-scale British birth cohorts, this paper investigates patterns of parent-care, care intensity and wellbeing at ages 38 and 42 (N = 17,255, N = 16,703; born 1970), 50 and 55 (N = 12,775, N = 11,339; born 1958) and 63 (N = 2,364; born 1946), how sibling composition intersects with gender in relation to care-giving and whether different care-giving patterns are associated with wellbeing. Only children are more likely to provide parent-care and the pattern is consistent with an interpretation that differences by sibling status might increase with age. Provision is gendered, and the sibling group composition matters for involvement. Although care-giving is related to wellbeing, we found no evidence that this differs between only children and those with siblings. The literature on only children has hitherto focused largely on childhood, suggesting that on some outcomes they benefit from a concentration of parental resources. Our results suggest that in middle adulthood parental care needs may instead be concentrated for the only child without the ‘resource’ of siblings. This indicates a need to develop further our understanding of this growing demographic subgroup.
This study evaluated the association between ultra-processed foods (UPF) on serum IL-6 and to investigate the mediation role of adiposity. Participants were 524 adults from the EPITeen Cohort (Porto, Portugal) and 2888 participants from the 1982 Pelotas Birth Cohort (Pelotas, Brazil). Dietary intake was collected using FFQ when participants were 21 years of age in the EPITeen and 23 years in the Pelotas Cohort. Serum IL-6 and body fat mass were evaluated when participants were 27 and 30 years old in the EPITeen and Pelotas, respectively. Generalised linear models were fitted to test main associations. Mediation of body fat mass was estimated using G-computation. After adjustment for socio-economic and behaviour variables, among females from the EPITeen, the concentration of IL-6 (pg/ml) increased with increasing intake of UPF from 1·31 (95 % CI 0·95, 1·82) in the first UPF quartile to 2·20 (95 % CI 1·60, 3·01) and 2·64 (95 % CI 1·89, 3·69) for the third and fourth UPF quartiles, respectively. A similar result was found among males in the Pelotas Cohort, IL-6 increased from 1·40 (95 % CI 1·32, 1·49) in the first UPF quartile to 1·50 (95 % CI 1·41, 1·59) and 1·59 (95 % CI 1·49, 1·70) in the two highest UPF quartiles. The P-value for the linear trend was < 0·01 in both findings. The indirect effect through fat mass was NS. Our findings suggest that the consumption of UPF was associated with an increase in IL-6 concentration; however, this association was not explained by adiposity.
This study aimed to determine the association of some demographic and clinical factors with recovery from olfactory and gustatory dysfunction in coronavirus disease 2019 patients in Iran.
Methods
This prospective cohort study was performed on 242 coronavirus disease 2019 patients with olfactory and gustatory dysfunction. The time from onset to recovery for olfactory and gustatory dysfunction was estimated by the Kaplan–Meier estimator.
Results
After six months, 239 patients (98.8 per cent) had completely recovered from olfactory dysfunction. Olfactory and gustatory dysfunction symptoms resolved in 80.99 per cent and 83.56 per cent of the patients, respectively, within the first 30 days of symptom onset. Mean recovery time for olfactory dysfunction (35.07 ± 4.25 days) was significantly longer in those infected during the first epidemic wave compared with those infected during the second wave (21.65 ± 2.05 days) (p = 0.004). A similar pattern in recovery time was observed for cases of gustatory dysfunction (p = 0.005).
Conclusion
The recovery rate for coronavirus disease 2019 related olfactory and gustatory dysfunction is high within the first month of symptom onset.