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Diabetes Increases Risk of Active TB

The finding comes from a systematic review of 13 observational studies looking at the link between diabetes and TB over the past four decades. In places such as India and China, where the background prevalence of TB is high, diabetes could account for as much as 10% of active cases, the researchers said in the online journal PLoS Medicine.

"We found consistent evidence for an increased risk of TB among people with diabetes," they said.
What’s more, the rise in type II diabetes — the current 180 million cases is predicted to rise to 366 million by 2030 — "does not bode well for the future" of TB control, the researchers said.

Physicians have noted an association between diabetes and active TB since the early part of the last century, but it has not been clear whether diabetes caused the TB or vice versa.

To help clarify the issue, the researchers conducted a systematic review of studies published from 1965 to 2007 that gave an age-adjusted quantitative estimate of the association between diabetes and active TB.

All told, they found 13 such studies, with 1.7 million participants — three prospective cohort studies, eight case-control studies, and two in which TB case accrual was prospective, but the underlying distribution of diabetes was determined later.
All three of the cohort studies — conducted in India, South Korea, and Taiwan — found a significant association between diabetes and active TB, with a summary relative risk of 3.11 and a 95% confidence interval from 2.27 to 4.26.

All eight case-control studies also showed an effect, with relative risks ranging from 1.16 to 7.83, but two of the confidence intervals crossed unity. One of the remaining two studies showed a relative risk of 6.0, with a 95% confidence interval from 5.0 to 7.2, but the other showed no effect, the researchers found.

Heterogeneity — or between-study variance — accounted for 39% of the total variance among the cohort studies, 68% among case-control studies, and 99% in the remaining two studies.

Despite that heterogeneity, the researchers said, the studies show "there is an increased risk of active TB among people with diabetes regardless of background incidence, study region, or underlying medical conditions in the cohort." They cautioned that the summary estimate of a 3.11 increase in relative risk is derived from cohort studies conducted in Asia, and may be different in other populations, depending on such variables as background TB prevalence and age.

Nevertheless, "it is clear that (diabetes) constitutes a substantial contributor to the current and future global burdens of TB," they said.

For example, assuming a relative risk of 3.0 and a 6% prevalence of diabetes in Mexico, the researchers calculated that diabetes accounts for 67% of active TB cases among those with diabetes, and 11% of cases among the entire Mexican population.
Practice Pearls:

  • Explain to interested patients that researchers have long noted an association between diabetes and active tuberculosis, but it has not been clear if the link is causal.
  • Note that this systematic review concluded that having diabetes, combined with a TB infection, increases the risk of developing active disease.

PLoS Medicine

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FACT:
Low-Carb and Low-Fat Diets Face Off: Major Study Ranks Low-Carb Diets Above the Rest.  The study is the latest round in the ongoing diet wars between the low-fat and low-carb diet rivals. Dr. Meir Stampfer, the study’s senior author and professor of epidemiology and nutrition at Harvard School of Public Health, told ABC News: "The low-carb diet was the clear winner in providing the most weight loss." While low-fat dieters lost an average of 7.3 pounds over the two-year period, those following the Mediterranean diet shed 10.1 pounds. The low-carb dieters peeled off the most weight, losing an average of 12.1 pounds.  The most surprising: people on the low-carb diet, even after two years of dining on meat and cheeses and eggs, did not have increased cholesterol levels. In fact, it actually lowered the cholesterol numbers of study participants. See this weeks’ Item #2

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