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Key concepts

Allostatic load

Causality debate

Food choices

Health impact assessment

Housing as health care

How social determinants shape health

Obesogenic environment

Race and health

Socioeconomic status (SES)

Allostatic load

What is it?

One of the great, unsolved mysteries in medicine is explaining why health and longevity tend to increase with socioeconomic status – even among those who are materially secure. There is no threshold at which the link between increasing SES and better average health comes to an end.

Access to health care and differences in health behavior, such as smoking and eating habits, only account for part of the link between socioeconomic status and health.

Allostatic load theory attempts to explain how psychological and social experiences “get under the skin” and give rise to disease. The basic idea is that repeated stressful experiences can build up over time, gradually wearing down the body’s regulatory systems, opening the door to the onset and progression of many different diseases.  Bruce McEwen and Teresa Seeman explain,

“For each system of the body, there are both short-term adaptive actions (allostasis) that are protective and long-term effects that can be damaging (allostatic load). For the cardiovascular system, a prominent example of allostasis is the role of catecholamines in promoting adaptation by adjusting heart rate and blood pressure to sleeping, waking, physical exertion. Yet, repeated surges of blood pressure in the face of job stress or the failure to shut off blood pressure surges efficiently accelerates atherosclerosis and synergizes with metabolic hormones to produce Type II diabetes, and this constitutes a type of allostatic load.”

Measures of allostatic load are supposed to reflect how well or poorly the cardiovascular, metabolic, nervous, hormonal and immune systems are functioning. Higher scores indicate greater vulnerability to illness.  Researchers have proposed different ways to score allostatic load. They combine the results of various tests: blood pressure, body mass index (or waist-hip radio), kidney function, blood sugar, cholesterol, C-reactive protein, and cortisol and other hormones that regulate the response to stress.

By combining multiple test results in one index, researchers are trying to capture the accumulated effect on all physiological systems, including feedback loops between those systems.

It’s possible that this approach might give researchers and public health officials a more immediate way to test the results of policies or programs designed to reduce health disparities. Because it may take years to see an impact on disease outcomes, some effective programs may appear to be ineffective if evaluated over too short a time horizon.

Evidence

People with higher allostatic load scores who have been tracked for years in observational studies are more likely to develop heart disease, experience cognitive and functional decline, and die prematurely.

Numerous studies have found that allostatic load builds up faster in people lower on the socioeoncomic ladder. Higher allostatic loads emerge as early as the first five years of life and persist throughout childhood, adulthood and older age. People living in disadvantaged neighborhoods have significantly more biological “wear and tear” as measured by allostatic load, above and beyond the effect of individuals’ income, education and race or ethnicity.

African Americans tend to have higher allostatic loads than white people, and higher poverty rates among blacks do not account for the difference. In fact, in one national analysis, high allostatic load scores were more prevalent among nonpoor blacks than among poor whites. The average score for blacks was roughly equal to the score for whites who were 10 years older.

Caveats

Current evidence does not provide definitive support for the proposed links between psychological and social stresses and dysregulation of biological systems. The field continues to debate which physiological measurements should be included in the allostatic load index. Some researchers question whether the indices used to score allostatic load are actually measuring the processes by which repeated stressful experiences shape health over the life course. In a recent study examining the elevated rate of poor birth outcomes among African American women, for example, allostatic load scores surprisingly did not correlate with preterm birth or low birth weight.

Further reading:

Causality debate

Research linking socioeconomic status and health is almost all observational, which means it shows correlation, not causation. So the research does not firmly establish that low income, lack of education or low social status cause poor health. Most often, the influences are likely to be reciprocal: social status affects health and health affects social status. Chronic illness, for instance, can hinder success in education, employment, and earnings.

Some authors assert that socioeconomic status is a proxy rather than a true cause of health inequalities, and emphasize behavioral risk factors that are under the control of individuals.

The debate is not merely academic. It’s still not clear, for instance to what extent investing in education or income transfers would improve population health. Attempts to use tax credits, income support, or school funding to improve health aren’t likely to work if income and education aren’t primary causes of the social gradient in health. If they are primary causes, solutions focused on individual behavior don’t stand much chance of success.

Further reading

Food choices

Income, education, neighborhood environment and other social forces shape and limit the food choices people make. 

For instance, studies consistently have found a socioeconomic gradient in food choices: at lower levels of socioeconomic status, the consumption of whole grains, lean meats, fish, low-fat dairy products, and fresh vegetables and fruit decreases while the consumption of fatty meats, refined grains, and added fats increases.

Cultural ways influence food preferences, such as the heavier meat consumption researchers have noted in low-income households. Investigators who interviewed nearly 100 low-income mothers in Minnesota found that ethnic traditions were influential, along with taste, meat’s versatility in meal preparation, and the importance of meat as a status symbol. Meat preferences also reveal how differing education plays a role. In recent years, Americans higher up on the ladder of education and income status have cut back on red meat consumption since it’s been tied to higher rates of cancer and other health risks. 

People living in lower income places also tend to be surrounded by less healthy offerings: fast food restaurants with “dollar” menus and corner stores selling snack foods rather than boutique green grocers and farmers’ markets selling fresh produce. Lower income neighborhoods also are subject to a heavier barrage of advertising  for unhealthy food and drink than wealthier neighborhoods.

Among people in lower income populations, price appears to be a significant driver of food choices. A recent meta-analysis by researchers at Brown University and the Harvard School of Public Health calculated that healthy eating costs about $1.50 more per day per adult than eating a low-quality diet ($550 more annually per person). That extra cost represents a 25 percent increase for a household that spends $6 per person on food each day, which is more than many low-income families spend. An earlier study found that the cost of substituting healthier foods can cost 35 to 40 percent of an American low-income family's food budget.

Energy-dense foods (made of processed grains, sugar, and fat) are typically the most affordable choices. Such fare also has a longer shelf-life, which is extra meaningful for people short on money and needing to minimize waste. Processed foods also cost less in terms of the time it takes to plan and prepare meals for those struggling to work long hours outside the home while handling childcare and housekeeping.

Some studies have shown that healthy food choices don’t necessarily have to increase household food spending. In a recent Canadian study, for example, researchers tracked 73 women who adopted a Mediterranean diet and found that it didn’t cost them more. But that study included mostly college educated women, all from households earning well above the poverty level. Studies including disadvantaged households (e.g. here and here) suggest that such families can often barely afford food, purchase most of their groceries at the lowest available prices, and would probably have to pay more to adopt healthier choices. 

Further reading:

Health impact assessment

Elected leaders and policy makers have opportunities to make choices that – if they take health into account – could help ameliorate public health problems such as the obesity epidemic and the large and growing disparities in the burden of chronic disease.

Health impact assessment, or HIA, is a way to scrutinize the effects a government program or project may have on the health of a population. The systematic process is supposed to help policy makers avoid unintended harmful effects and take advantage of opportunities to promote health.

According to the The Health Impact Project, an initiative of the Robert Wood Johnson Foundation and The Pew Charitable Trusts, "HIA gives federal, tribal, state and local legislators, public agencies and other decision makers the information they need to advance smarter policies today to help build safe, thriving communities tomorrow."

The number of assessments has mushroomed from a few dozen in 2007 to more than 240 completed or in progress in 35 states, Washington, D.C., Puerto Rico, and at the federal level as of 2013, according to a recent Institute of Medicine report.

Examples:

After a health impact assessment in Alaska, the Bureau of Land Management in 2007 withdrew part of an oil and gas development lease that threatened the health of native populations, and the approved lease required new pollution monitoring and controls.

A health impact assessment helped resolve concerns about a proposed biomass energy project in Placer County, Calif., in 2012. The assessment found that the project would likely benefit community health in the Lake Tahoe Region through the removal of forest slash and reduction of wildfire fuels, the diversion of open pile burns to more emission efficient combustion and the diversification of energy sources.

Boston’s regional transit agency in 2013 held off imposing steep fare increases and service cuts after a health impact assessment concluded that it would lead to significant health and financial costs because of increased automobile use.

How they’re done:

Assessments generally follow a six-step process.

1. Screening: Decide whether a HIA is warranted and would be useful in the decision-making process.

2. Scoping: Choose which health impacts to evaluate, the methods for analysis, and a workplan for completing the assessment.

3. Assessment: Gather data and predict health impacts using qualitative and quantitative research methods.

4. Recommendations: Prioritize evidence-based proposals to mitigate negative health impacts and maximize positive health impacts.

5. Reporting: Communicate findings.

6. Monitoring: Evaluate the effects of the impact assessment on the decision-making process.

Challenges:

The Robert Wood Johnson Foundation recently analyzed 23 health impact assessments completed between 2005 and 2013. Most weren’t given enough time or money, the authors concluded. People doing the assessments struggled to find relevant, neighborhood-level data, and they found it tough to make headway in politically charged situations. In some cases, agencies moved ahead on project decisions without waiting for completion of the health impact assessment.

Further reading:

Housing as health care

People who are homeless face many health threats and are among the heaviest users of hospital services. Safe and affordable housing, some experts assert, is a necessary first step to care effectively for people with chronic mental health and substance abuse problems who live on the streets. And there is some evidence that this approach may, in some circumstances, even save taxpayers money (but probably not as much as is often claimed).

In an influential 2009 study in Seattle, researchers analyzed medical and law enforcement costs for 91 people given supportive housing and found that costs dropped to about half the level seen among 35 comparable homeless people on a waiting list. But note that this savings estimate doesn’t include the capital costs of building and refurbishing apartments. Raising capital is likely to be a tall hurdle for many communities and this issue often gets ignored in news reports about the promise of supportive housing.

News coverage sometimes overstates the potential cost savings. In a study of supportive housing in Chicago, the savings were statistically insignificant. In a five-city study, clients in supportive housing wound up costing more than a comparison group of people not given housing.

Some advocates assert that saving money is an unfair requirement for a medical intervention that effectively relieves suffering. The cost-effectiveness of medical interventions is customarily measured in terms of quality-adjusted life-years gained, not dollars saved.

Housing First, a model developed by New York-based Pathways to Housing and others, has occasionally provoked controversy because of its “harm reduction” approach. Tenants are not required to take part in rehab or abstain from drugs or alcohol to remain eligible.

Some outstanding questions include:

  • Can cities fund addiction treatment services and mental health treatment adequately to serve everyone in supportive housing who seeks help?

  • How will proposed supportive housing stand up to NIMBY opposition from neighbors?

  • How should housing agencies handle residents who continue to use illegal drugs? What if the residents who continue to drink or use drugs have children living with them?

  • How will service agencies decide who will qualify for supportive housing? The available housing units aren’t likely to accommodate more than a fraction of the people in need.

Further reading

How social determinants shape health

Education, income, and social status appear to shape health in a complex web of interactions. Habits such as smoking, inactivity, poor diet and substance abuse are more prevalent among people in disadvantaged social groups, and probably account for much of the health gap between people of different social classes.

But behavior is not just a matter of personal choices. People are buffeted by social, cultural, and economic forces that can strongly influence behavior. In some disadvantaged neighborhoods, for example, tobacco and liquor advertising is prominent, lack of safe or convenient parks discourages outdoor recreation and much of the affordable food offered for sale is unhealthy.

Educational opportunity and achievement are especially powerful influences. Adults without a high school diploma, for example, are three times more likely to smoke than college graduates. Lesser education correlates with many other unhealthy behaviors. Education acts in at least two ways: It equips people with knowledge and skills useful for prevention of disease, and it paves the way to secure employment, a decent income and higher social status.

The physical environment and social quality of neighborhoods are important variables. People in lower-income and minority neighborhoods are likely to face more environmental health risks, such as hazardous waste sites and air pollution from nearby factories and highways. Such neighborhoods may lack social cohesion, undermining residents’ sense of security and well-being. Living in a neighborhood with high unemployment, urban blight and crime imposes a burden of chronic stress.

Prolonged exposure to stress can trigger the release of hormones, such as cortisol and epinephrine, that undermine immunity, boost inflammation and increase vulnerability to conditions such as diabetes and heart disease. Stress during fetal development, from a mother’s poor diet or exposure to pollutants, for example, may set the stage for diseases decades later in life by altering metabolism or triggering lasting changes in the activity of genes. Some studies suggest that these “epigenetic” changes in gene expression can be passed on to children and influence the occurrence of disease in more than one generation.

Further reading

Obesogenic environment

Some of the social changes we’ve allowed – or even embraced – make it difficult for people to avoid unhealthy weight gain in the U.S. One of the most vivid demonstrations of our obesogenic environment is what happens among successive generations of immigrants: one recent study of Mexican immigrants found that the risk of becoming obese tripled by the second generation, relative to peers who remained in their native land.

Relative odds of obesity for women migrating from Mexico to the U.S. (Source: Mexico–United States Migration and the Prevalence of Obesity: A Transnational Perspective, Karen R. Flórezet al, JAMA Internal Medicine 2012)

Here are some of the environmental factors behind the rapid rise of obesity in the U.S. since the 1980s:

Food production & marketing
Food companies spend over a billion dollars a year marketing nutrient-poor, calorie-dense convenience meals and snacks to children, producing measurable changes in food preferences and eating habits. U.S. Farm subsidies have boosted the output of nutrient poor, energy-dense food and pushed down the prices relative to healthier options. From 1985 to 2000, retail prices of fresh vegetables and fruit rose nearly 120 percent, about six times more than the rate of increase for soft drinks and three times more than that of sweets and fats.

Child development
Obesity is the outcome of a process that can start in fetal development and infancy. An expectant mother’s severe undernourishment, or substantial
overnourishment, can alter fetal metabolism and brain development, making offspring more prone to obesity, according to a number of animal and human studies. During infant development, observational studies have linked bottle-feeding rather than breast-feeding to weight gain. Lack of sleep, a trend affecting even toddlers, appears to promote obesity by disturbing the regulation of the hormones that drive appetite and the body's rate of energy use. In the Early Childhood Longitudinal Study, which tracked 7,738 kindergartners for a decade starting in 1998, half of the cases of obesity that arose were among kids who had become overweight during the preschool years.

Built environment
Unsafe streets and lack of green space may be barriers to being physically active, although the
evidence is limited. The effects of income and education may trump the influence of the built environment. It is clear that a lack of physical activity is one of the key factors in the worsening obesity gap between haves and have-nots. Children of college-educated parents have became more active than they were a decade ago, while children of less educated parents showed no improvement, according to a recent analysis.

Access to healthy food
People living in lower income neighborhoods tend to be surrounded by less healthy offerings, i.e., fast food restaurants and corner stores selling convenience foods rather than green grocers and farmers’ markets selling fresh produce. Lower income neighborhoods may also be subject to a heavier barrage of advertising for unhealthy food and drink than higher income neighborhoods. To what extent “food deserts” drive obesity remains unclear. But the high price of healthy food does appear to be a significant driver of
fattening food choices among families with limited incomes.

Further reading:

Race and health

Life expectancy and mortality data reveal a complexity in the way race, ethnicity and gender combine to affect health risks. Compared to white Americans, African Americans and American Indians have higher death rates at every age from birth until advanced age. But black women have higher levels of life expectancy than white men at every age. Hispanics in the U.S. have lower mortality than whites at older ages. And Asians have lower mortality rates throughout life. 

Racial disparities in health have persisted for decades – and in some cases worsened. Infant mortality for African Americans was 1.7 higher than for whites  1940, and despite steep reductions in infant deaths, the gap between blacks and whites has widened such that the rate among blacks was 2.4 times higher than whites as of 2006. In 1950, black and white Americans had comparable death rates for heart disease and cancer, but now death rates for both diseases are significantly higher among blacks.

Socioeconomic status
Blacks and Hispanics have levels of overall poverty that are two to three times higher than those of whites. And socioeconomic inequalities have changed little over time, contrary to perception.  But even after taking socioeconomic status into account, many disparities in health remain. A study comparing white physicians from Johns Hopkins University with black physicians from Meharry Medical College found large racial differences in health. Diabetes and hypertension were twice as high among the black doctors, who also had higher rates of heart disease than the white doctors.

“Weathering hypothesis”
One cause of ethnic and racial disparities could be greater exposure to adverse social conditions and physical environments, which leads to greater wear and tear on physiological systems. Comparisons of infant death rates supply intriguing evidence to support this so-called “weathering hypothesis.” Among white and Mexican American women, infant mortality rates are lower for mothers who give birth in their twenties compared to those in their teens. But it’s the opposite for African American and Puerto Rican women in the U.S., who experience the lowest infant mortality as teenagers and higher infant mortality in their twenties,  perhaps as a result of accumulated stress. 

A revealing study compared African Americans and whites on measure called “allostatic load,” which is supposed to reflect how well or poorly the cardiovascular, metabolic, nervous, hormonal and immune systems are functioning. Scores are based on readings of blood pressure, body mass index, kidney function, blood sugar, cholesterol,  C-reactive protein and other tests. The study found that blacks scored worse than whites at all ages, and the racial differences persisted after adjustment for poverty. In fact, nonpoor blacks scored worse than poor whites.

Racism
Recent studies have found links between discrimination and health outcomes including sleep disturbance, abdominal fat, high blood sugar, coronary artery calcification, and breast cancer. Acceptance of negative stereotyping by stigmatized groups can be a source of anxieties that undermine social and psychological functioning. This so-called “internalized racism” has been linked to excessive drinking and psychological distress among African Americans. But as it stands, only a few studies have attempted to pin down the role of discrimination as a cause of health disparities.

Medical care
Blacks in the United States are two to three times more likely than whites to have diabetes-related amputations, but blacks living in the U.K. face no higher risk than whites. Some experts believe that the near universal access to primary care in the U.K. accounts for the difference.  There is evidence suggesting that prevention-oriented health care can help reduce disparities in health.

Costa Rica is an eye-opening case study. The country’s infant death rates fell from 60 per 1,000 live births in 1970 to 19 per 1,000 live births in 1985. Researchers attribute most of the improvement to public health programs, particularly the build up of primary health care in underserved areas in the 1970s. For each five years after primary care reform, child mortality fell by 13 percent, and adult mortality fell by 4 percent.

Experts in the field of social determinants of health tend to minimize the importance of medical care. (One widely quoted estimate asserts that medical care account for just 10 percent of potentially avoidable deaths.) But some research indicates that medical care may achieve bigger positive changes among socially disadvantaged populations than among the well-off.

Further reading:

 

Socioeconomic status (SES)

Health studies routinely attempt to account for socioeconomic status, which is a person’s place in the hierarchy of wealth, self-determination, prestige and power. Socioeconomic status, or SES, is strongly linked to health and longevity. People higher on the SES ladder tend to live longer and healthier lives than people lower on the ladder. This link, the SES-health gradient, persists even among people in the middle and upper ranges of social position, many studies have shown.

To account for socioeconomic status, researchers typically rely on proxy measures such as years of education or household income. It’s convenient to do so, and sometimes no better data is available.

However, it’s important to keep in mind that proxy measures can obscure substantial socioeconomic differences.

Studies that compare people by househould income, for instance, are blind to potentially very large differences in wealth. Wealth, or total accumulated economic resources, is a stabilizing force that buffers families from the effects of setbacks such as unemployment or illness. People with comparable income can have drastically different wealth. Among very low income households, those headed by whites have about 400 times as much wealth as those headed by blacks. At higher income, whites have about 3 to 9 times the wealth of blacks.

Using years of education as a proxy can overlook meaningful differences in the quality of education. In some disadvantaged neighborhoods and cities, the quality of public schools is drastically worse than average. Also, years of education is definitely not a reliable stand-in for income or wealth. In the U.S., for example, black adults with 12 years of schooling earn 33 percent less, on average, than white adults with the same level of education, while Mexican-Americans earn 18 percent less than whites. Racial and ethnic disparities in income persist at every level of educational attainment, possbily as a result of unequal employment opportunities and differences in educational quality.

One-time measures of socioeconomic status ignore the effect of past experiences. Socioeconomic status can change over the course of a life, and past episodes of poverty or dramatic loss of income can have long-lasting effects on health. Deprivation during fetal development and early childhood, for example, can increase vulnerabilty to disease decades later.

Focusing on proxy measures of individuals may fail to register the influence of the different neighborhoods where people live.  The characteristics of the built environment and social fabric of a neighborhood are powerful enough to shape health above and beyond the individual’s socioeconomic status.

In an informative review article worth reading in its entirety, Dr. Paula Braveman and colleagues distilled some useful conclusions about difficulties of accounting for socioeconomic status:  

• Proxy measures of socioeconomic status are not interchangeable.  

• Proxy measures can miss important and relevant aspects of socioeconomic status, and even studies that include multiple measures cannot capture all of the potentially important socioeconomic influences on health.

• A given proxy measure may have different meanings depending on the race, ethnicity, age, sex, or neighborhood environment of the people being considered.

• Racial and ethnic health disparities are likely to reflect unmeasured socioeconomic differences. (But that doesn’t mean that racial and ethnic disparities are reducible to socioeconomic issues; discrimination may also be an active force.)

Further reading:


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