Analysis of the Association between Metabolic Syndrome and Disease in a Workplace Population over Time

Background

Individuals with metabolic syndrome (MetS) are at increased risk of morbidity and mortality from a variety of health conditions, thus making MetS an important trait to recognize and treat. The definition of MetS changed over the past decade as researchers identified the most critical risk factors. The first widely used definitions were developed by the World Health Organization [1] and the National Institutes of Health [2]. Currently, the best regarded definition of MetS is that of the American Heart Association and National Heart, Lung and Blood Institute [3], which has a high utility in determining those at risk. Their definition confirmed the value of the Adult Treatment Panel III criteria [2] with some minor modifications, making the current standard for MetS risk criteria based on the following: waist circumference (≥102 cm in men, ≥88 cm in women, or body mass index [BMI] > 30 kg/m²), triglycerides ≥150 mg/dl, high-density lipoprotein [HDL] cholesterol (<40 mg/dl for men or <50 mg/dl for women, or taking cholesterol medication), blood pressure (≥130/85 mmHg or blood pressure medication), and fasting glucose (≥100 mg/dl or glucose medication).

Because MetS is characterized by many of the accepted risk factors of cardiovascular disease (CVD), the former is thought to be a strong predictor of the latter. In fact, many researchers have found that the risks of developing CVD (and subsequent death) are higher among those with MetS compared to those without the syndrome [4–13]. But, because of the obvious overlap between MetS and CVD risk factors, some argue that MetS does not provide any additional information about cardiovascular risk factors [14]. Others contend that the combined effect of these risk factors is greater than the sum of its parts, and that knowledge of MetS is helpful and informative in predicting CVD [14].

Individuals with MetS are also at a higher risk of developing diabetes (five times higher in one study [14]) compared to those without MetS [15–17]. Again, this is not unexpected because of the MetS risk factor of elevated fasting glucose levels, a characteristic of diabetes. Other medical conditions found to be associated with MetS include the chronic pain condition fibromyalgia [18], carpal tunnel syndrome [19–21], asthma [22], and polycystic ovary syndrome [23,24].

None of these previously mentioned studies, however, were conducted in a worksite population. Corporations are the main payers of health-care costs in the United States; thus, they have a more vested interest than corporations in other countries in identifying the magnitude of MetS risk factors in employed populations and in knowing if these risks are associated with other health risks or medical conditions. Many companies offer wellness programs to encourage their employees to maintain a healthy lifestyle, thereby reducing health risks such as those that define MetS.

This study identified the prevalence of MetS risk factors in employees of a large manufacturing corporation who participated in a health risk appraisal (HRA) screening in 2004 and again in 2006. The presence of disease was assessed through self-report at time 1 in 2004 and at time 2 in 2006 to see if MetS risk factors were associated with increased rates of disease in an employed population. Furthermore, health-care costs, pharmacy costs, and short-term disability (STD) costs were measured among those who met the criteria for MetS, but did not yet have an associated disease to see if the risk factors alone are associated with higher costs.

Methods

Results

MetS Risk Factors and Prediction of Disease

In Table 5, we present the odds ratios and 95% confidence intervals for several multiple logistic regression models.

Table 5. Odds of incident disease* in 2006 for those with each MetS risk factor in 2004

Risk factor in 2004	Arthritis in 2006 OR (95% CI)	Chronic pain in 2006 OR (95% CI)	Diabetes in 2006 OR (95% CI)	Heartburn in 2006 OR (95% CI)	Heart disease in 2006 OR (95% CI)
Obesity	2.100	1.695	3.831	1.105	1.475
	(1.442–3.060)	(1.091–2.633)	(1.970–7.450)	(0.751–1.625)	(0.747–2.912)
Hypertension	1.463	1.004	3.829	1.021	2.071
	(0.977–2.146)	(0.635–1.588)	(1.869–7.841)	(0.695–1.500)	(1.033–4.150)
Glucose	1.261	0.707	15.257	1.169	1.372
	(0.849–1.874)	(0.996–1.044)	(5.834–39.902)	(0.789–1.734)	(0.685–2.747)
HDL	1.346	1.467	3.048	1.193	2.687
	(0.917–1.977)	(0.943–2.280)	(1.605–5.788)	(0.818–1.738)	(1.371–5.265)
Triglycerides	1.737	2.621	3.749	1.294	1.559
	(1.183–2.551)	(1.650–4.164)	(1.791–7.848)	(0.894–1.873)	(0.785–3.097)
MetS	1.999	1.607	13.191	1.172	2.355
	(1.359–2.940)	(1.021–2.530)	(5.428–32.059)	(0.789–1.741)	(1.187–4.673)

• * Logistic regression adjusted for age and gender.
• HDL, high density lipoprotein cholesterol; MetS, metabolic syndrome.

We found that people who met the risk criteria for obesity and triglycerides in 2004 were significantly more likely to self-report new cases of arthritis in 2006 (P-value <0.05). These same risk factors were significantly associated with the incidence of chronic pain in 2006 as well (P-value <0.05). All five of the risk factors were associated with the incidence of diabetes, while none were significantly associated with new cases of heartburn. Finally, hypertension and HDL were associated with the incidence of heart disease 2 years later (P-value <0.05). MetS was significantly associated with the prediction of four out of five of the conditions (arthritis, chronic pain, diabetes, and heart disease) with odds ratios ranging from 1.607 for chronic pain to 13.191 for diabetes, after controlling for age and gender.

Figure 1 shows the costs (health care, pharmacy, and STD) for each of four groups in 2006: those without MetS or any of the five associated diseases; those with MetS but no disease; those without MetS but with a disease; and those with both MetS and a disease.

The average cost increases from a baseline of $1600 for employees without MetS and without any of the five diseases included here (arthritis, chronic pain, diabetes, heartburn, or heart disease). The next group of employees, those with MetS but none of the diseases, had an average cost of $2037. Those without MetS but at least one of the five diseases had an average cost of $4113 which was significantly higher than the previous two groups. Finally, those with both MetS and at least one of the diseases had the highest costs of $5857 which was significantly higher than the other three groups. This figure shows the high costs associated with disease among employed individuals.

The next analysis repeated the previous figure but limited the diseases to just diabetes and heart disease. Results are similar to the results found in Figure 1 with the highest costs occurring in the last two groups: those without MetS but who have diabetes or heart disease, and those with both MetS and at least one of those diseases (Fig. 2).

Discussion

The prevalence of MetS in this employed population is slightly higher than the prevalence found in nationally representative studies reporting rates of 23% to 25% [27,28]. Nevertheless, our study uses the most recent definitions of MetS which include people taking medication for glucose, triglycerides, HDL, and/or hypertension. The prevalence of MetS in this two-time participant population increased significantly from 2004 to 2006. The authors of another study of the NHANES data sets from 1988 to 1994, and from 1999 to 2000 have also indicated that rates of MetS are increasing in the United States [30].

As in other studies [27,28], employees who met the criteria for MetS were significantly older and more likely to be male than those without MetS. Other demographic differences in education level, income, marital status, and ethnicity were not significant after controlling for age and gender.

The main topic of this study was the relationship between MetS and disease in a working population. Those with MetS in 2004 were significantly more likely to report having arthritis, chronic pain, diabetes, heartburn, heart disease, and stroke in 2004 compared to those without MetS, after controlling for age and gender differences. Diabetes and heart disease are obviously associated, given the overlap between the risk factors for MetS and those for these two conditions. There is also evidence in the literature that chronic pain conditions are associated with MetS. In one study, fibromyalgia was associated with larger waist circumference, higher glycosylated hemoglobin and triglyceride levels, and higher blood pressure [18]. The association found with heartburn and MetS may simply be an effect of the strong association between obesity and heartburn. The association with stroke has not been noted in the literature, but given the similar risk factors for heart disease and stroke, it is not surprising that a relationship with MetS would be identified. The very small prevalence of stroke in this working population limits the generalizability of these results, however.

Employees with MetS in 2004 were significantly more likely to report new cases of arthritis, chronic pain, diabetes, and heart disease, but not heartburn. To minimize the level of disease among employees, organizations should address MetS and its health risks. Rates of diagnosed diabetes are increasing in the United States [31,32], and working populations are no exception. Nevertheless, worksite health management programs have been shown to be effective in helping “prediabetic” employees reduce their risks to prevent full-blown diabetes even after 2 years of follow-up [33].

After examining these associations between MetS and disease, it was appropriate to examine the associated costs (health care, pharmacy, and STD). The cost of those with MetS and disease were 3.66 times greater than those without MetS and without disease. Results indicate that disease is certainly a significant factor in determining the costs associated with MetS. All of those with disease had higher costs than those without disease, but those with both MetS and disease had the highest cost of any group. What is most interesting to employers is the fact that employees with MetS but who had not yet developed one of the five health conditions had slightly higher costs, but they were not yet significantly different from the employees without MetS and without disease.

When the cost analysis was limited to just heart disease and diabetes, those with MetS and disease had costs five times higher than those without MetS and without disease, and four times higher than those with MetS but who had not yet developed diabetes or heart disease. Again, the encouraging finding for organizations is that the majority (88%) of those with MetS in this population had not yet developed diabetes or heart disease, and 67% had not yet developed any of the five conditions studied in Figure 1 (arthritis, chronic pain, diabetes, heartburn, or heart disease). The largest opportunity is in helping these individuals improve their risks so that those conditions are prevented.

There is an opportunity for health promotion to prevent the MetS risk factors from progressing to disease status which may improve vitality for employees, as well as limit the economic impact to the corporation. An integrated approach to mitigating the effects of health risks might include several components [34–37].

Employers should implement educational and screening programs for their employees to prevent undiagnosed or misdiagnosed illnesses which will allow employees to better manage their medical conditions. The Wellness Council of America estimates that an effective, comprehensive program can cost about $100 to $150 per employee per year [38]. In addition to lower-cost educational programs, it is also necessary for employers to spend money on improving employee medical treatment to improve workplace productivity.

Previous studies have found associations between MetS and health conditions such as depression [39,40], and kidney disease [41] which were not identified in the current analysis. Because of the particular demographics of this working population (83% men, with an average age of 40.8 years), it may be unlikely to detect the association between MetS and depression which has primarily been studied in female samples. For example, only 3.5% of the study population self-reported depression compared to national statistics of major depression affecting 6.6% of the adult US population in any 1 year [42]. Furthermore, because this is a population of working adults rather than a patient population, the rates of certain diseases such as kidney disease would be small or nonexistent. This is likely because of the healthy worker effect (HWE). The HWE most often is discussed in mortality studies because actively employed individuals consistently have a lower mortality rate than the general population [43]. Nevertheless, it also applies to studies such as this which examine disease and other health condition prevalence among employed individuals [44–46].

Limitations

This study is typical of most worksite health promotion studies in that the design is cross-sectional and retrospective. The ideal study design (i.e., a randomized, controlled study) is difficult or impossible to conduct in a worksite population because of the relationship between employees and employer. Another common limitation of worksite analyses is that the HRA participants are not representative of the entire employee population. Because of the near universal participation rate at this company, the population studied is very likely to be representative of the corporation as a whole although we are assuming that those who did not participate did so at random and that they represent nonimformative missing data. The results are unique to this corporation, however, and similar studies should be conducted in a variety of worksite industries to see if the findings are replicated in different demographic groups.

As was mentioned, waist circumference was not measured, so BMI was used as a surrogate. The current criteria of MetS states that if an individual has a BMI greater than 30 kg/m², we can safely assume that his or her waist circumference exceeds the risk level [25]. Nevertheless, it does leave the possibility that individuals with BMI < 30, but with central adiposity which meets the waist circumference risk cut point would not be identified here. A future study will compare the use of waist circumference and BMI as risk factors for MetS because the company added waist circumference to its screening in 2007.

The information on medical conditions in this study relied on self-reporting of participants. Each individual's criteria for reporting a certain condition may not have matched typical diagnostic criteria for each condition. Previous studies of self-report data have shown that relying on self-report for medical conditions can be a valid method [47–49], although in one study patients reported more conditions than could be verified in medical charts [50].

Conclusions

This study provides employers, health-care providers, and public health professionals with more information about the extent of MetS and its consequences in working populations. The medical conditions arthritis, chronic pain, diabetes, heartburn, and heart disease were significantly more prevalent in employees with MetS than those without MetS. Indeed, individuals with MetS but no disease in 2004 were more likely to newly report four of those five conditions (arthritis, chronic pain, diabetes, and heart disease) 2 years later. It was unknown whether the diseases associated with MetS in the general population would also be found in a working population because of the HWE [51] but it does appear to be the case.

Moreover, this study highlights the opportunity that is available to organizations seeking to improve the health of employees. While employees with MetS and a medical condition had significantly higher costs than other employees, the vast majority of employees with MetS in this study had not yet developed one of the five medical conditions studied here, and their costs were not significantly greater than those without MetS. If individuals take advantage of programs helping them to both maintain their low risks and reduce their high risks, their odds of experiencing disease will be reduced. This leads to improved vitality and quality of life for individuals, and cost avoidance for corporations in the form of lower health care, pharmacy, and STD costs.