Effects of n-3 polyunsaturated fatty acids on glucose homeostasis and blood pressure in essential hypertension. A randomized, controlled trial.

OBJECTIVE

To determine whether dietary supplementation with fish oil adversely affects glycemic control in patients with hypertension.

DESIGN

Randomized, double-blind, placebo-controlled study.

PATIENTS

78 persons with untreated hypertension recruited from a population survey.

INTERVENTION

Participants were randomly assigned to receive eicosapentaenoic and docosahexaenoic acids, 4 g/d, or corn oil placebo, 4 g/d, for 16 weeks.

MEASUREMENTS

An oral glucose tolerance test; assessments of insulin release, glucose disposal, and insulin sensitivity done using the hyperglycemic clamp technique to keep plasma glucose levels at 10 mmol/L for 180 minutes; assessment of insulin sensitivity done using a euglycemic hyperinsulinemic clamp technique (infusing insulin and glucose to keep plasma glucose levels at 5 mmol/L); assessments of lipid levels and blood pressure. Measurements were done before and after intervention.

RESULTS

Changes in integrated glucose and insulin response after the oral glucose challenge did not differ between the fish oil and corn oil groups after intervention (-0.6 +/- 0.7 compared with -1.0 +/- 0.6 mmol/L [P > 0.3] for integrated glucose and 143 +/- 76 compared with 169 +/- 84 pmol/L [P > 0.3] for insulin response). Changes in first-phase insulin release (34 +/- 72 pmol/L in the fish oil group compared with 191 +/- 112 pmol/L in the corn oil group [P > 0.3]), second-phase insulin release (179 +/- 66 pmol/L compared with 257 +/- 122 pmol/L [P > 0.3]), and insulin sensitivity index (-0.03 +/- 0.01 compared with -0.01 +/- 0.01 [mumol/kg.min divided by pmol/L]; P > 0.3) were also similar in both groups after treatment. Fish oil lowered systolic blood pressure by 3.8 mm Hg more than control (P = 0.04) and lowered diastolic blood pressure by 2.0 mm Hg more than control (P = 0.10). After fish oil treatment, triglyceride levels decreased by 0.28 +/- 0.08 mmol/L more than control (P = 0.01), and very-low-density lipoprotein cholesterol levels decreased by 0.13 +/- 0.04 mmol/L more than control (P = 0.01).

CONCLUSION

Fish oil, in doses that reduce blood pressure and lipid levels in hypertensive persons, does not adversely affect glucose metabolism.