Stroke Rounds: Amino Acid in High-Protein Foods May Lower Stoke Risk

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http://www.medpagetoday.com/Cardiology/Strokes/50674?xid=nl_mpt_cardiodaily_2015-03-26&
High dietary intake of the non-essential, sulfur-containing amino acid cysteine was linked to lower stroke risk in a study of women living in Sweden.
High-protein foods such as beef, poultry and eggs are major sources of cysteine in the diet. Eating a high-protein diet has been linked with lower blood pressure and stroke risk in some studies, and the new research may explain this association, researcher Susanna C. Larsson, PhD, of the Karolinska Institute in Stockholm, and colleagues wrote in the journal Stroke.

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Women whose diets included the highest levels of cysteine had a 21% lower risk of stroke compared with women whose diets included the least amount of the amino acid.
"Our results further suggest that dietary cysteine may account, at least in part, for our previous observed inverse associations of total protein and animal protein intake with risk of stroke," the researchers wrote.
Dietary Protein and Blood Pressure
The data connecting dietary protein with blood pressure remain confusing.
A meta-analysis of 40 studies, published in 2012, found higher protein consumption to be associated with significant decreases in systolic and diastolic blood pressure and in a study from Boston University School of Medicine, published in 2014, researchers reported similar findings.

That study included participants in the Framingham Offspring Study between the ages of 30 and 54. Eating a high protein diet that was also high in fiber was associated with a 59% reduction in hypertension risk.
Other studies suggest that eating a primarily vegetarian, lower-protein diet is associated with lower blood pressure, including a meta-analysis of seven controlled trials and 32 observational studies published in 2014.
The newly published research expands on a 2012 study by Larsson and colleagues which found higher dietary protein intake to be inversely associated with stroke risk in women with hypertension.
"In this study we evaluated the a priori hypothesis that cysteine intake is inversely associated with risk of stroke, and that cysteine may have contributed to our previous observed finding for dietary protein," they wrote.
Only Cysteine Inversely Associated with Stroke Risk

Using data from the Swedish Mammography Cohort, which is a population-based prospective cohort of 34,250 women, the researchers identified 1,751 stroke cases during 10.4 years of follow-up. Cysteine intake was assessed through food frequency questionnaires, and the women also provided information on BMI, smoking status and history, and other relevant lifestyle factors.
Compared to women in the lowest quartile of cysteine intake (<559 mg/d), those with the highest intake (>703 mg/d) tended to be older, had a higher BMIs and were less likely to be current smokers and more likely to have a history of hypertension or diabetes.
Cysteine intake was found to be significantly inversely associated with risk of total stroke after adjustment for other stroke factors and total protein intake.
Among the findings:

• Comparing the highest and lowest quintile of cysteine intake, the multivariable relative risk of total stroke was 0.79 (95% CI 0.65-0.97; P=0.04 for trend).
• The corresponding relative risk was 0.82 (95% CI 0.65-0.97; P for trend = 0.12) for cerebral infarction and 0.54 (95% CI 0.29-1.03; P=0.08 for trend) for intracerebral hemorrhage.
• Dietary intake of other amino acids, including proline and arginine, showed no independent association with stroke risk.

Potential study limitations cited by the researchers included the fact that food frequency and lifestyle questionnaires were self administered. But they noted that given the prospective study design, measurement error in assessing amino acid intake would be unlikely to be related to outcomes.

They further noted that because the study was observational, it cannot prove cause and effect. Several previous studies examining the association between amino acid intake and stroke risk have failed to show a protective role for dietary cysteine with regard to blood pressure.
"We observed an inverse association between dietary cysteine intake and risk of stroke," the researchers concluded. "Our findings further suggest that cysteine, at least partly, may account for the reported inverse relation between animal protein intake and stroke risk. These results warrant confirmation by other prospective studies and randomized trials."