PHILADELPHIA (FRONTLINE MEDICAL NEWS)– Long-term intake of meat and poultry is independently associated with an increased risk of developing hypertension, according to findings from an analysis of pooled data from three large prospective cohort studies.

The data also suggest that long-term intake of seafood does not protect against hypertension, Dr. Lea Borgi of Brigham and Women’s Hospital, Boston reported at Kidney Week 2014.

Of approximately 122,000 women in the Nurses’ Health Study 1, 116,000 women in the Nurses’ Health Study II, and 52,000 men in the Health Professionals Follow-up Study, those with an intake of at least 1 serving daily of meat and poultry (processed meat, beef, lamb, chicken, or turkey) and those with at least 1 serving daily of meat, poultry and seafood (including canned tuna, dark meat fish, shrimp, and lobster) had a greater risk of hypertension than did those with an intake of less than 1 serving monthly (hazard ratios, 1.30 and 1.22, respectively), Dr. Borgi said.

Seafood alone was associated with an increased risk of hypertension in the Nurses’ Health Study 2 (hazard ratio 1.13) and in the Health Professionals Follow-Up Study (hazard ratio, 1.16).

“Now, given that the association of seafood with hypertension was unexpected, we did do a secondary analysis … and we actually were able to analyze different types of seafood such as canned tuna fish, dark meat fish, other fish, shrimp, lobster, or scallops,” she said.

Those who consumed 4-6 servings a week of canned tuna or dark meat fish had an increased risk of hypertension (hazard ratio, 1.13 and 1.24, respectively), she said.

Study subjects ranged in age from 27 to 75 years, and information about diet, behaviors, and health status was updated regularly in each of the studies. The subjects were followed for a mean of about 20 years.

The current analysis was adjusted for numerous hypertension risk factors, including known risk factors like age and body mass index, and factors shown to be associated with hypertension in the cohorts, including analgesia use and consumption of sugar-sweetened and artificially-sweetened beverages. Adjustment was also made for total consumption of fruits, vegetables, and grains, as decreased consumption of these foods may also be associated with hypertension. Random effects meta-analysis was used to derive pooled estimates of effect.

Prospective data on the relationship between red meat, seafood, and poultry consumption and hypertension are scarce, but red and processed meats are generally considered to have an adverse effect on cardiovascular health, while seafood is generally believed to be protective; the effect of poultry is controversial, as study results have been conflicting, Dr. Borgi said.

“Our finding that more meat intake was associated with increased risk of hypertension is broadly consistent with prior studies. We also found that a greater consumption of poultry was independently associated with increased hypertension risk, and we observed a weak increased risk of hypertension with increasing fish consumption overall,” she said, noting that the mechanisms for the relationship are “controversial and hypothetical,” and include a possible relationship between gut microflora and cardiovascular disease, which is supported by a growing body of evidence.

“One of these links is through the conversion of L-carnitine, which is highly found in red meat and salt water fish, to trimethylamine N-oxide (TMAO). Also, another potential mechanism is the production of Maillard reaction products (MRPs), which are chemical products that are formed when animal flesh is cooked at high temperatures,” she said, explaining that TMAO and MRPs are associated with increased oxidative stress and inflammation, which are important mechanisms in the development of hypertension.

Given the increasing prevalence of hypertension in the United States and around the world, the independent and significant association between higher intakes of meat, poultry, and seafood and greater risk of developing hypertension seen in this study has important public health implications, she said, adding that additional studies are needed to further assess the potential mechanisms underlying the association.

Dr. Borgi reported having no disclosures.

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