Influence of Herring (Clupea harengus) Intake on Risk Factors for Cardiovascular Disease

Doktorsavhandling, 2008

This thesis describes four studies that investigated whether or not herring (Clupea harengus) intake decreases cardiovascular disease (CVD) risk factors. It has previously been shown that fatty fish and fish oil intake decreases the risk of atherosclerosis and CVD. However, until these studies, no research has investigated influence of herring intake on CVD risk factors. Herring has high eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content and are rich in other nutrients, such as vitamins D and B12, selenium and various antioxidants that may affect CVD risk factors. One of the aims with this thesis was to study how both the whole herring meat and its individual constituents (the oil and water fraction) affect CVD risk factors. Studies I and II were crossover intervention studies with 4- and 6-week dietary periods, respectively. Study I had 13 obese men and women; study II had 35 overweight men; the subjects received five meals per week that included 150 g baked herring fillets or, as controls, 150 g baked lean pork or chicken fillets. Plasma lipoproteins and other CVD risk factors, such as C-reactive protein, oxidized-LDL and blood pressure, were measured. The herring-rich diet significantly raised HDL in both studies, compared with the control diets. Pooled data from the two human intervention studies together showed that the oxidized -LDL/LDL ratio was significantly lower in subjects on a herring rich diet. In study III, 96 rats were fed six different diets to investigate whether the addition of herring or subfractions of herring could counteract negative metabolic effects known to be induced by a high-fat, high-sugar diet. Risk factors for metabolic syndrome were evaluated after the diets. In rats, herring and herring oil resulted in an improved lipoprotein profile and decreased triacylglycerides. Herring oil decreased the adipocyte size, indicating that herring oil could decrease the risk for type 2 diabetes mellitus. Herring water fraction and herring decreased plasma oxidation products (thiobarbituric acid reactive substances [TBARS]). Study IV used carotid intima-media thickness to evaluate the extent of subclinical atherosclerosis. Plasma phospholipid EPA and DHA were measured in a population-based cohort of 61-year-old men (n=487). EPA was negatively associated with intima-media thickness in the carotid and femoral arteries. EPA and DHA levels were also negatively associated with several CVD risk factors, such as markers of endothelial function. These data indicated that subjects with the metabolic syndrome or obesity, who commonly have low HDL, may benefit from the addition of herring to their diet. The studies demonstrated that high fish intake had a neutral or slightly positive effect on oxidative status.