Blood pressure and adipose tissue linoleic acid

Association of omega-6 polyunsaturated fatty acids with blood pressure: A systematic review and meta-analysis of observational studies

OBJECTIVES

This systematic review and meta-analysis aimed at summarizing earlier findings on the association of n-6 PUFAs levels in diets or blood with blood pressure.

METHODS

PubMed/Medline, Scopus, and Web of Science were searched for observational studies. Publications with data on the risk of hypertension, or the correlation between n-6 PUFAs or mean values of serum n-6 PUFAs levels in normotensive and hypertensive were included.

RESULTS

Twenty-two studies (16 cross-sectional studies, 5 cohorts and one case-control) were eligible. Combining 14 extracted effect sizes showed that higher circulatory/dietary n-6 PUFAs tended to be associated with 10% lower risk of HTN (95% CI: 0.81, 1.00), whereas combining 23 effect sizes illustrated no difference in circulatory/dietary n-6 PUFAs mean levels between normotensive and hypertensive subjects. According to subgroup analysis based on fatty acid types, total n-6 PUFAs (OR = 0.82, 95% CI: 0.70, 0.97) and linoleic acid (OR = 0.56, 95% CI: 0.39, 0.82) were inversely related to the risk of HTN. Circulatory/dietary n-6 PUFAs were correlated neither with systolic nor with diastolic blood pressure.

CONCLUSIONS

Higher circulatory/dietary n-6 PUFAs tend to be associated with lower odds of HTN. Particularly, total n-6 PUFAs and linoleic acid were associated with lower risk of HTN.

The role of serum monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) in cardiovascular disease risk

Free fatty acids (FFA) observed as independent risk factors of cardiovascular diseases (CVD). In this study we investigated FFA levels in patients with CVD, and its risk factors. In this case-control study, 214 patients experienced coronary angiography and 222 healthy subjects were enrolled. Participants were categorized into two groups: who had >50% and <30% stenosis were assigned to the angiogram positive (N=90) and negative (N=124) group, respectively. Several risk factors were assessed and the levels of FFAs were determined using gas chromatography. Serum FFA concentrations were compared between healthy and patients with positive and negative angiograms. The association of serum FFA levels with four major risk factors (hypertension, FBG level, high BMI and WHR) were also assessed. Our data showed that median of FFAs was higher in patients than healthy subjects (p<0.0001), such as SFA and n6-FFAs (in patients; 1.59 (1.27) and 1.22 (1.06) and in healthy subjects 0.33 (0.38) and 0.36 (0.35), respectively). According to anthropometric and biochemical data, there were not statistical differences between the groups, except FBG, SBP and hs-CRP that showed significantly higher levels in patients than controls (p<0.0001, p=0.001). Also, lower median levels of total cholesterol, LDL-C, HDL-C and DBP were observed in patients which can due to lipid-lowering medication use like Statins. High serum levels of FFAs are considered as an independent risk factor for CVDs, while various types of FFAs can have different influences on CVD risk factors. Therefore, longitudinal studies are needed to clarify the association between FFAs and CVD risk factors. (www.actabiomedica.it)

Is there an association between serum cholesterol and blood pressure changes?

A community-based programme to influence the risk factors of coronary heart disease was carried out in North Karelia, Eastern Finland in 1972-77. The evaluation, based on examination of large cross-sectional random samples at the outset and at the end of the period, showed a greater reduction in both serum cholesterol and blood pressure levels in North Karelia than in a matched reference area. A random cohort of 293 men and 321 women who were studied both in 1972 and in 1977 did not use antihypertensive drugs on either occasion. Among these people the change in blood pressure was positively associated with the change in serum cholesterol even when age, initial blood pressure, changes in body mass and number of blood pressure measurements were allowed for. This finding supports the hypothesis that changes in fat consumption lead to changes in blood pressure, but this hypothesis needs further investigation.

Dietary factors and hypertension

There is increasing evidence that nutritional factors are critical in the pathogenesis of essential hypertension typical for acculturated societies. These factors include sodium, potassium, calcium, alcohol, and type and level of fat in the diet. More research is needed, however, before the role of various nutrients in the prevention and treatment of hypertension will be ascertained.

Dietary saturated and unsaturated fats as determinants of blood pressure and vascular function

The amount and type of dietary fat have long been associated with the risk of CVD. Arterial stiffness and endothelial dysfunction are important risk factors in the aetiology of CHD. A range of methods exists to assess vascular function that may be used in nutritional science, including clinic and ambulatory blood pressure monitoring, pulse wave analysis, pulse wave velocity, flow-mediated dilatation and venous occlusion plethysmography. The present review focuses on the quantity and type of dietary fat and effects on blood pressure, arterial compliance and endothelial function. Concerning fat quantity, the amount of dietary fat consumed habitually appears to have little influence on vascular function independent of fatty acid composition, although single high-fat meals postprandially impair endothelial function compared with low-fat meals. The mechanism is related to increased circulating lipoproteins and NEFA which may induce pro-inflammatory pathways and increase oxidative stress. Regarding the type of fat, cross-sectional data suggest that saturated fat adversely affects vascular function whereas polyunsaturated fat (mainly linoleic acid (18 : 2n-6) and n-3 PUFA) are beneficial. EPA (20 : 5n-3) and DHA (22 : 6n-3) can reduce blood pressure, improve arterial compliance in type 2 diabetics and dyslipidaemics, and augment endothelium-dependent vasodilation. The mechanisms for this vascular protection, and the nature of the separate physiological effects induced by EPA and DHA, are priorities for future research. Since good-quality observational or interventional data on dietary fatty acid composition and vascular function are scarce, no further recommendations can be suggested in addition to current guidelines at the present time.

Serum fatty acids and blood pressure

To examine the relation between serum fatty acids and blood pressure, we conducted a cross-sectional study of 156 men who were enrolled in the Multiple Risk Factor Intervention Trial. After confirming the stability of the stored serum samples, we measured serum fatty acid levels by gas-liquid chromatography and examined their association with blood pressure. Using stepwise linear regression, we determined that each SD increase (1.9%) in the serum level of cholesterol ester palmitoleic acid (16:1) was associated with a systolic pressure increase of 3.3 mm Hg (95% confidence interval, 0.9 to 5.6 mm Hg) and each SD increase (0.1%) in phospholipid omega 9 eicosatrienoic acid (20:3) was associated with a diastolic pressure increase of 1.7 mm Hg (95% confidence interval, 0.5 to 2.9 mm Hg). Serum level of cholesterol ester steric acid (18:0) was inversely associated with diastolic pressure: each SD increase (0.2%) was associated with a decrease of 1.4 mm Hg (95% confidence interval, -2.5 to -0.2 mm Hg). In multivariate models that included dietary fat intake, cholesterol ester dihomogammalinolenic acid (20:3) was also associated with diastolic pressure: each SD increase (0.16%) was associated with an increase of 1.2 mm Hg (95% confidence interval, 0.1 to 2.4 mm Hg). Our results indicate that three nonessential fatty acids--stearic acid, palmitoleic acid, and omega 9 eicosatrienoic acid, and one essential fatty acid--dihomogammalinolenic acid, are independent correlates of blood pressure among middle-aged American men at high risk of coronary heart disease.

Fatty acid composition of adipose tissue in humans. Implications for the dietary fat-serum cholesterol-CHD issue

Interest in studies of the fatty acid composition of adipose tissue has arised from the dietary fat-serum cholesterol-CHD issue. The fatty acid composition of depot fat reflects that of the diet. Gas chromatography analysis of subcutaneous adipose tissue yield objective and reliable information of the fatty acid composition of the habitual diet of individuals. A relative linoleic acid deficiency, as depicted by low adipose tissue linoleate levels, has not convincingly been demonstrated to be of importance in the aetiology of atherosclerosis or related disorders. Inverse correlation between n-3 fatty acids and coronary artery disease has been reported. Dietary supplementation of n-3 fatty acids may be of relevance, however the risk of hazardous side-effects do exist. In conclusion, a simple reduction of the total fat content of the diet still seems to be the most important strategy for prevention of atherosclerosis.

Dietary fats, antioxidants and blood pressure

Although obesity and alcohol intake as well as dietary sodium, potassium and magnesium are the major non-genetic determinants of blood pressure levels, interest has recently been stimulated in the function of fatty acids and antioxidants in the aetiology of hypertension. In the Kuopio Ischaemic Heart Disease Risk Factor Study both plasma ascorbic acid and serum selenium concentrations had a moderate, independent inverse association, estimated dietary intake of saturated fatty acids had a positive association and estimated dietary intake of linolenic acid had an inverse association with the mean resting blood pressure in 722 Eastern Finnish men with neither self reported hypertension nor cerebrovascular disease. Even though these cross sectional observations do not prove causality, they warrant clinical trials to verify or disprove that dietary fats and antioxidants are factors in the development of hypertension.

Effect of a monounsaturated diet vs. a polyunsaturated fatty acid-enriched diet on blood pressure in normotensive women and men

The effect on blood pressure of monounsaturated and (n-6)polyunsaturated fatty acids was studied under strict dietary control in normotensive subjects. For 17 days 31 women and 27 men received a control diet providing 19.3% of energy as saturated fat. Then subjects were randomized over two test diets: one diet provided 15.1% of energy from monounsaturated and 7.9% from polyunsaturated fatty acids ('mono diet'), and the other diet provided 10.8% from monounsaturated and 12.7% from polyunsaturated fatty acids ('poly diet'). Saturated fat intake was now 12.8% on both diets. Mean blood pressure at the end of the control period was 116/69 mmHg for the mono group and 117/73 mmHg for the poly group. After 5 weeks on the test diet, blood pressure was 115/67 mmHg for the mono group and 117/72 mmHg for the poly group (difference in changes between the two diet groups was not significant). These findings suggest that at a high fat intake, linoleic acid, when providing more than 7.9% of energy intake, does not influence blood pressure relative to oleic acid in normotensive women and men.

Relationship of dietary fat to plasma fatty acids, blood pressure, and urinary eicosanoids in adult men

This experiment was conducted to determine the relationships between modest changes in dietary linoleate, blood pressure (BP) response, and levels of eicosanoid synthesis in humans. Products of eicosanoids which appear in blood were measured in urine: PGI2, 6-keto-PGF1 alpha (KPGI2); TXA2, (TXB2); PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha, (MPGF2 alpha). Twenty-three adult men were fed controlled diets having 25 energy percent fat, and having P/S ratios of either 0.3 (low-PUFA) or 1.0 (high-PUFA), for a total of 12 weeks, with a switchover between P/S ratios at 6 weeks. The results showed that, under the conditions of this study, BP was significantly reduced by reducing dietary fat intake from about 37 to 25 energy percent. However, no further effects on BP were produced by increasing the P/S ratio from 0.3 to 1.0. KPGI2 excretion was significantly lowered on both controlled diets as compared to the self-selected (SS) diet. However, MPGF2 alpha was lowered only on the low-PUFA diet as compared to the self-selected diet. No significant decrease in TXB2 excretion was observed. Both MPGF2 alpha and KPGI2 excretion were positively correlated with urine volume and sodium excretion. On the SS diet, but not on the controlled diets, MPGF2 alpha excretion was negatively correlated with plasma linoleate and positively correlated with stearate. On the low-PUFA diet, MPGF2 alpha excretion increased with the intake of linoleate, while, on the high-PUFA diet, it decreased. This may have been due to the limited amounts of linoleate available in the low-PUFA diet (3.2-3.4 energy percent) as compared to that in the high-PUFA diet. Both KPGI2 and MPGF2 alpha excretion were positively correlated with systolic and diastolic BP. These results suggest that the amount of dietary linoleate is an important factor in the regulation of prostaglandin synthesis in humans.

Prostaglandins, brown fat and weight loss

In obesity, a situation is created in which energy intake exceeds energy expenditure. The three components of energy expenditure are resting metabolism, physical activity, and thermogenesis. Increasing attention is being paid to the role of impaired energy expenditure in obesity. Evidence indicates that impairment in activity of the sympathetic nervous system, which stimulates thermogenic processes, contributes to the etiology of obesity. In addition, insulin resistance, a well-recognized metabolic consequence of obesity, appears to interfere with feeding-related, insulin-mediated increases in thermogenesis in brown adipose tissue. This thermogenic defect results in reduced energy buffering by brown adipose tissue leading to deficient energy expenditure and an increased efficiency in weight gain. A unique weight loss program, The Princeton Metabolic Diet Program, is presented. The Program stimulates metabolism by stimulating the sympathetic nervous system and correcting insulin resistance, thereby enhancing thermogenesis in brown adipose tissue. Methods include: 1) alternating diet composition and caloric intake and, 2) the use of nutritional metabolic stimulants. This type of non-toxic therapy, directed at correcting biochemical defects, will enhance metabolic mechanisms and induce weight loss.

Cardiovascular actions of dietary polyunsaturates and related mechanisms. A state-of-the-art-review

A survey of the effects of dietary polyunsaturates on the function of the cardiovascular system is given. In isolated hearts of rats dietary linoleate supply increases both coronary flow and heart muscle function. Hearts of rats fed high amounts of linoleic acid are protected against catecholamine (over)-stimulation. Polyunsaturate rich vegetable oils are effective in lowering blood pressure in several murine hypertension models. This effect seems to be closely related to antihypertensive changes in kidney function and in the function of the arterial vessel wall. Dietary polyunsaturates augment the hypotensive effect of antihypertensive drugs. Cardiovascular effects of dietary polyunsaturates are at least partly mediated via changes in the prostanoid metabolism as well as a reduction of the sympathetic activity. Evidence has been accumulated that cardiovascular effects of dietary polyunsaturates in animal and man are comparable. The observed effects are discussed against the background of a reduced risk of cardiovascular disease after a polyunsaturate rich diet in man.

Dietary fat and blood pressure: an intervention study on the effects of a low-fat diet with two levels of polyunsaturated fat

The role of dietary fat in human blood pressure control was studied among 84 middle-aged subjects (mainly couples) in two semirural communities in North Karelia, Finland. The families were randomly allocated into two groups that, after a baseline period of 2 weeks, changed their diet for a 12-week intervention period so that the proportion of energy derived from fats was similarly reduced in both groups, from 38 to 24%, but the polyunsaturated/saturated fatty acid (P/S) ratio was increased--from 0.2 to 0.9 in group I and to 0.4 in group II. After the intervention period, both groups switched back to their usual diet for a period of 5 weeks. During the intervention period, total serum cholesterol was reduced by 16% in group I and 14% in group II. Mean body weight and urinary sodium, potassium, calcium, and magnesium excretion changes were small or nonexistent. Mean systolic blood pressure decreased 4 mm Hg in group I (P less than 0.01) and 3 mm Hg in group II (P less than 0.01), and mean diastolic blood pressure decreased 5 mm Hg (P less than 0.001) and 4 mm Hg (P less than 0.01), respectively. The reductions were reversed during the switch-back period (P less than 0.01). These results confirm previous findings of the blood-pressure-reducing effect of a low-fat/high-P/S diet. Although a number of possible confounding factors can be ruled out, the dietary constituent accounting for the blood pressure change cannot be ascertained definitely. The results showed no significant further blood pressure reduction with more than a moderately increased P/S ratio when the saturated fat intake was markedly reduced.

Essential fatty acids in the liver and adipose tissue of genetically obese mice: effect of supplemental linoleic and gamma-linolenic acids

Genetically obese mice (ob/ob) and their lean litter-mates were given diets iso-energetically supplemented with sucrose, hydrogenated coconut oil, safflower oil or evening primrose (Oenothera biennis) oil. Weight gain over 15 weeks was significantly greater in the evening primrose oil-supplemented obese mice than in the other groups. In all the groups of obese mice, liver total phospholipids contained proportionally less linoleic acid and more dihomo-gamma-linolenic acid and arachidonic acid than did the lean controls. As a percentage of total fatty acids, n-3 essential fatty acids (EFA) in liver and adipose tissue lipids were significantly lower in the obese mice than in the lean controls. Supplementation with EFA-rich oils (safflower and evening primrose oil) increased the proportional composition of n-6 EFA and decreased the n-3 EFA more in the liver total phospholipids of the lean than the obese mice.

Relation of blood pressure to reported intake of salt, saturated fats, and alcohol in healthy middle-aged population

The association of blood pressure with reported intake of salt, saturated fats, and alcohol was studied in a sample of 8479 subjects based on a cross sectional survey in a population aged 30 to 64 years. A consistent association was found between the mean arterial pressure and the intake of alcohol (p less than 0.001) and saturated fats (p less than 0.01). There was also a weak association between blood pressure and dietary salt intake, but this association was mostly explained by the correlation of salt intake with alcohol and saturated fats. The observed relationships support the hypothesis that blood pressure is influenced by diet.

Inverse relationship between linoleic acid in serum and in adipose tissue of patients with essential hypertension

In patients with labile essential hypertension without and with overweight as well as in normotensive controls the fatty acid pattern of serum triglycerides and subcutaneous adipose tissue was estimated by gas liquid chromatography. In serum triglycerides of hypertensives linoleic acid was increased but appeared decreased in depot fat. This inverse relationship could not be found for arachidonic acid. Correspondingly, the C 18:2/C 20:4-ratio was higher in serum triglycerides than in adipose tissue. Only in depot fat of overweight hypertensives the percentage of arachidonic acid was decreased when compared to subjects with normal body weight. Linolenic acid remained unchanged in serum triglycerides but decreased significantly in adipose tissue of hypertensive patients. Eicosapentaenoic acid was increased in serum triglycerides and depot fat of patients with essential hypertension of normal body weight. The results are discussed with respect to the possible pathogenesis of essential hypertension and the hypotensive potency of dietary linoleic acid which has been described in patients with high blood pressure.

Fatty-acid composition of serum lipids predicts myocardial infarction

During a follow-up of five to seven years 33 out of 1222 middle-aged men initially free of coronary heart disease sustained fatal or non-fatal myocardial infarction or died suddenly. The fatty-acid composition of serum triglycerides, phospholipids, and cholesterol esters had been measured at the start of the surveillance in these men and in a control group of 64 men matched for age, serum cholesterol and triglyceride concentrations, blood pressure, obesity, smoking, and one-hour glucose tolerance. Palmitic and stearic acids of phospholipids were significantly higher and linoleic and most polyunsaturated fatty acids, including arachidonic acid and eicosapentaenoic acid, of phospholipids were lower in the subjects who sustained coronary events compared with the controls. Linoleic acid tended to correlate negatively with blood pressure while other polyunsaturated fatty acids, especially eicosapentaenoic acid, exhibited a negative correlation with blood pressure and relative body weight in the controls but not in the subjects who sustained coronary events. These findings suggest that the fatty-acid pattern of serum phospholipids is an independent risk factor for coronary heart disease.

Evening primrose oil, a dietary prostaglandin precursor, diminishes vascular reactivity to renin and angiotensin II in rats

Polyunsaturated fatty acids (PUFA) are biosynthetic precursors of prostaglandins (PG). Endogenous biosynthesis of PG in vessel wall and kidney contributes to the regulation of arterial blood pressure. By increasing the fraction of PUFA in the diet systemic blood pressure can be lowered while PUFA deficient diet leads to an increase in blood pressure. To evaluate the effect of an enhanced PG biosynthesis by dietary PG precursors on vascular reactivity and vascular formation of prostacyclin-like activity, the pressor response to intravenous renin and angiotensin II in rats pretreated p.o. for 3 months with evening primrose oil (EPO, 1 ml/day) was determined and the antiaggregatory activity released by aortas of treated rats studied. EPO is unique in that it contains beside linoleic acid (72%), gamma-linolenic acid itself (9%). In contrast to olive oil treated rats EPO pretreatment diminished vascular reactivity to the vasopressor stimuli of renin and angiotensin II and increased the formation of vascular prostacyclin-like activity (p less than 0.05). These studies imply the possibility of a selective modulation of PG production by dietary maneuvers.

Blood pressure and diet in normotensive volunteers: absence of an effect of dietary fiber, protein, or fat

In the course of four controlled experiments on the effect of specific dietary components on cardiovascular risk factors, the effects on blood pressure of various sources of dietary fiber, of type and amount of dietary fat, and of animal versus plant were measured in young normotensive volunteers. In each of the four experiments a group of 50 to 75 healthy student volunteers received a control diet for 11/2 to 21/2 wk. They were then randomized into subgroups which received various test diets for periods ranging from 4 to 12 wk. In each experimental one group received the control diet throughout the whole experimental period. Diets differed between groups in one dietary component only. All foodstuffs were weighed out individually according to each person's energy needs. Body weights and Na intake were controlled. Initial blood pressures were about 120 mm Hg systolic and 70 mm Hg diastolic. Both systolic and diastolic blood pressure decreased during the test period in all four experiments on almost every diet, including the control diets, by about 0 to 5 mm Hg. However, changes in blood pressure over the test period were never significantly different between the test groups and the control groups. Thus, none of the investigated dietary factors had a demonstrable effect on blood pressure in young normotensive persons.

Physical training and adipose tissue fatty acid composition in men

Four months physical training significantly raised the mean proportions (%) of lauric (+0.64), myristic (+0.52), stearic (+2.06) and linoleic (+1.69) acids and lowered the mean proportions of palmitic (-1.46) and oleic (-3.46) acids in adipose tissue of 20 apparently normal men aged 20-55 yr. These changes were dependent on pretraining proportions of the fatty acids. In addition, the decreases in palmitic acid and oleic acid proportions were positively correlated (rho = 0.905, P less than 0.01, tau = 0.758, P less than 0.01). The pattern of significant correlations among adipose tissue fatty acids was altered as a result of training. We suggest that preferential mobilisation of fatty acids from adipose tissue is responsible for the change in adipose tissue fatty acid composition with increased physical training. The significant increase in adipose tissue linoleic acid proportions may be linked with the reduced risk of coronary heart disease which has been previously associated with increased physical activity.

A new concept of lifestyle-related cardiovascular disease: the importance of interactions between cholesterol, essential fatty acids, prostaglandin E1 and thromboxane A2

A proposal to account for the inter-relationships between established risk factors and cardiovascular disease is presented. In this concept, the critical substance is prostaglandin (PG) E1 which is a vasodilator, an inhibitor of platelet aggregation, an inhibitor of cholesterol and collagen biosynthesis and an inhibitor of smooth muscle proliferation. PGE1 biosynthesis is enhanced by the essential fatty acid, linoleic acid, by the platelet aggregating agent thromboxane (TX) A2, by cholesterol and by melatonin. These factors may participate in a negative feedback control loop. As a result of the operation of this loop, any tendency for PGE1 levels to fall is followed by increased cholesterol and TXA2 biosynthesis, and enhanced platelet aggregation, vasoconstriction, smooth muscle proliferation and collagen biosynthesis. Enhancement of PGE1 biosynthesis will have the opposite effects. Factors known to increase PGE1 biosynthesis include essential fatty acids, vitamin C, ethanol, pyridoxine, zinc and probably niacin, all of which are known to have some protective effects against cardiovascular disease. The hypothesis predicts that lowering of cholesterol biosynthesis by any method other than enhanced PGE1 formation, while reducing the risk of cardiovascular disease, will increase the risk of other disorders. The hypothesis suggest new approaches to treatment and new ways of combining existing treatments. Colchicine, which at low concentrations may imitate and action of melatonin, has particularly interesting possibilities. Colchicine and related compounds have already been shown to have potent cholesterol-lowering and anti-atherogenic actions in both humans and animals.