Omega-3 polyunsaturated fatty acids and risk of type 1 diabetes in
children
DENVER, COLORADO. Dietary factors have been implicated in the etiology of type 1 diabetes, a disease that
frequently occurs during childhood. In a study from Norway, cod liver oil was implicated in preventing this type of
diabetes, but it was unclear whether the effect was due to the omega-3 fatty acids, vitamin D or some other
constituent. In a study just reported, Norris et al report on an observational study of dietary intake of omega-3 fatty
acids and the incidence of pancreatic islet autoimmunity (IA) in a group of children judged at high risk of type 1
diabetes because of family history or the presence of an identified genetic predisposition. One group studied
consisted of children recruited between birth and 8 years of age who had strong family history of type 1 diabetes. A
second group consisted of newborns who tested positive for genetic markers of susceptibility. The association
between intake of omega-3 and omega-6 fatty acids and the incidence of IA was examined during the follow-up. It
was found that higher intake of omega-3 fatty acids was associated with a significant decrease in the risk of IA in
the group identified by family history. For the newborn group, the risk of IA was inversely associated with the
omega-3 status assessed by a blood test. These associations were relatively strong and statistically significant.
Omega-6 fatty acids were not found to beneficial or harmful in this context. The authors comment that that if these
results are confirmed in an ongoing intervention study involving supplementation with DHA in utero and in infancy,
then omega-3 fatty acids could become a mainstay for early intervention to safely prevent the development of type
1 diabetes in this high-risk group of children.
Norris, J.M. Omega-3 Polyunsaturated Fatty Acid Intake and Islet Autoimmunity in Children at Increased Risk for
Type 1 Diabetes. Journal of the American Medical Association, 2007, Vol. 298, No. 12, pp. 1420-28
Fish oils benefit women with diabetes
BOSTON, MASSACHUSETTS. Several studies have found a clear inverse association between the
consumption of fish and fish oils and the risk of coronary heart disease (CHD) and sudden cardiac death.
However, it is not known whether this protective effect extends to diabetes patients. Researchers at the
Harvard Medical School have just concluded a study to examine this. Their study included 5103 female
nurses with diabetes, but free of cardiovascular disease and cancer at entry. Between 1980 and 1996
there were 362 cases of CHD (7.1%) and 468 deaths from all causes in the study group (9.2%). The
causes of death were CHD or stroke – 161, cancer – 172, and other causes – 135.
Study participants completed detailed food frequency questionnaires in 1980, 1984, 1986, 1990 and
1994. The researchers noted a strong correlation between the risk of CHD and fish intake. Women who
consumed fish once a week had a 40% lower risk of CHD than did women who consumed fish less than
once per month. Eating fish 5 times per week reduced CHD risk by 64% and overall mortality by 52%.
Only dark-meat fish (mackerel, salmon, sardines, bluefish, and swordfish) and shrimp, lobster and
scallops showed a beneficial effect. The researchers also calculated the amount of fish oils
(eicosapentaenoic acid and docosahexaenoic acid) obtained from the diet and found that study
participants with an average intake of just 250 mg/day had a 31% reduction in CHD and a 37% reduction
in death from all causes compared to participants with a low (40 mg or less) daily intake. The researchers
note that fish oil supplementation does not impair glycemic control and suggest that regular fish
consumption should be considered as an integral part of a healthy diet for the management of
diabetes.
Hu, Frank B., et al. Fish and long-chain omega-3 fatty acid intake and risk of coronary heart disease and total
mortality in diabetic women. Circulation, Vol. 107, April 15, 2003, pp. 1852-57
Grundy, Scott M. N-3 fatty acids: priority for post-myocardial infarction clinical trials. Circulation, Vol. 107, April 15,
2003, pp. 1834-36 (editorial)
Editor's comment: Swordfish, bluefish and king mackerel have high levels of mercury or methyl
mercury and should not be eaten regularly, if at all.
Fish oil supplementation is safe for diabetics
PARIS, FRANCE. People suffering from type II diabetes often have high blood levels of triglycerides and
are therefore prone to coronary heart disease. Fish oils are known to be effective in lowering triglyceride
levels, but concern has been expressed that they may also increase low-density lipoprotein (LDL) levels
and be deleterious to glucose control.
Medical researchers at the Hotel-Dieu hospital now report the results of a study designed to investigate
these concerns. The study involved 10 men with type II diabetes (average age of 54 years). The men
were randomized into two groups in the double-blind crossover study. Group 1 supplemented with 6
grams/day of fish oils (containing 320 mg of eicosapentaenoic acid [EPA] and 215 mg of
docosahexaenoic acid [DHA]) for two months while group 2 supplemented with 6 grams/day of sunflower
oil (containing 65% linoleic acid). At the end of the two months all participants went through a 2-month
wash-out period and group 1 was then assigned to supplement with sunflower oil while group 2 was given
fish oil supplements. All participants maintained their regular diet (55% carbohydrates, 15% protein, and
30% fat) and continued with their medications throughout the study except for cholesterol-lowering drugs
which were discontinued 2 months before the start of the trial.
The researchers noted a considerable increase in both EPA and DHA content in blood plasma
phospholipids and in red blood cell membranes after two months on the fish oil supplements. Triglyceride
levels and the level of plasma lipoprotein(a) were both significantly lowered following fish oil
supplementation. No adverse effects on glucose control were observed; there was a small increase in
the LDL level, but this was compensated for by a similar increase in the HDL (high-density lipoprotein)
level so that the important LDL/HDL ratio remained unchanged. The researchers conclude that fish oil
supplementation is effective in lowering triglyceride levels in type II diabetics and has not adverse effects
on glycemic control or overall cholesterol levels.
Luo, Jing, et al. Moderate intake of n-3 fatty acids for 2 months has no detrimental effect on glucose
metabolism and could ameliorate the lipid profile in type 2 diabetic men. Diabetes Care, Vol. 21, May
1998, pp. 717-24
Fish oils and fiber benefit diabetics
CLEVELAND, OHIO. Patients with non-insulin-dependent diabetes mellitus (NIDDM) often suffer from
abnormal lipid (fat) and lipoprotein metabolism resulting in unfavourable cholesterol levels and an
accompanying increase in the risk of heart disease. Numerous studies have shown that fish oil
supplementation lowers the levels of very-low-density-lipoprotein (VLDL) and triglycerides
(triacylglycerol), but has little effect on the levels of low-density-lipoprotein (LDL) and total cholesterol.
There has also been some reports that fish oil supplementation may worsen glycemic (glucose) control.
Now medical researchers at the Case Western Reserve University report that adding soluble fiber to the
fish oil supplementation regimen is highly beneficial. Their experiment involved 15 non-obese NIDDM
patients (12 men and 3 women) aged 32 to 74 years. For the first four weeks the patients received 20
grams of fish oil per day (equivalent to six grams of n-3 fatty acids). During the next four weeks all
patients received the fish oil plus 15 grams/day of soluble apple pectin. During the final four weeks both
supplements were withdrawn. The patients continued their usual diabetic diet and medication during the
entire study period. Analysis of blood samples showed that fish oil supplementation alone lowered the
levels of triacylglycerol and VLDL cholesterol by 41 per cent and 36 per cent respectively. No changes
were observed in total cholesterol, LDL cholesterol or HDL cholesterol. When apple pectin was added to
the treatment triacylglycerol and VLDL cholesterol levels were both lowered by 38 per cent, but in addition
total cholesterol levels decreased by 13 per cent and LDL cholesterol by 7 per cent. There was no
significant change in HDL cholesterol level. Fasting and two-hour postprandial plasma glucose
concentrations were not affected by the fish oil or fish oil/pectin supplementation and no changes in
serum levels of zinc, magnesium, and copper were observed. Plasma levels of triglycerides and
cholesterols returned to pre-treatment levels four weeks after discontinuation of supplementation. The
researchers conclude that a combination of fish oil supplementation and increased fiber intake (up to 40
grams/day total) may be a beneficial addition to the conventional treatment of high cholesterol levels in
NIDDM patients.
Sheehan, John P., et al. Effect of high fiber intake in fish oil-treated patients with non-insulin-dependent
diabetes mellitus. American Journal of Clinical Nutrition, Vol. 66, November 1997, pp. 1183-
87
Diabetics may benefit from fish oil supplementation
NAPLES, ITALY. Animal studies have shown that fish oil supplementation has a beneficial effect on
insulin resistance and can prevent its development in animals fed a high-fat diet. It is also known that a
high fish intake can delay the development of diabetes in glucose-intolerant individuals. Researchers at
the Federico II University recently set out to investigate if long-term supplementation with fish oils would
improve insulin sensitivity in patients with non-insulin-dependent diabetes (NIDDM). The clinical trial
involved 16 NIDDM patients (average age of 56 years) who, after a 3 week run-in period during which
they received 3 olive oil capsules per day, were assigned to receive either fish oil capsules or olive oil
capsules for a further 6-month period. For the first two months the participants received either 3 fish oil
capsules daily (320 mg eicosapentaenoic acid [EPA] and 530 mg docosahexaenoic acid [DHA] per
capsule) or 3 placebo capsules (each containing 1 gram of olive oil). During the last four months these
dosages were reduced to 2 fish oil or 2 placebo capsules daily. The patients were evaluated at the
beginning and end of the trial and maintained their usual diet and medications (except for cholesterol-
lowering drugs) during the entire trial period.
The researchers concluded that fish oil supplementation induced a significant decrease in triglyceride
concentrations particularly in the level of very-low-density lipoprotein (VLDL) triglycerides (a reduction of
45%). There was also a significant decrease in VLDL cholesterol levels (47% drop) and a 14% increase
in LDL cholesterol. There was no significant change in blood glucose control and, contrary to
expectations, no significant improvement in insulin resistance despite the fact that red blood cell levels of
EPA and DHA increased significantly. The researchers conclude that long-term fish oil supplementation
lowers triglyceride levels in NIDDM patients without adversely affecting blood glucose control. NOTE:
This study was partially funded by Pharmacia, Farmitalia Carlo Erba, Milan, Italy.
Rivellese, Angela A., et al. Long-term effects of fish oil on insulin resistance and plasma lipoproteins in
NIDDM patients with hypertriglyceridemia. Diabetes Care, Vol. 19, November 1996, pp. 1207-13
Diabetes and fish oil supplementation
EDMONTON, CANADA. Diabetics are at significantly increased risk for cardiovascular disease and any
dietary intervention that could decrease this risk would be of great importance. Studies have shown that
fish oil supplementation lowers triglycerides, very low density lipoprotein (VLDL) levels, and blood
pressure in non-diabetic individuals and thereby diminishes their risk of heart disease. Unfortunately,
some early experiments with fish oil supplementation in type II diabetics reported adverse effects on
glycemic control and cholesterol levels.
Researchers at the University of Alberta have just released the results of a new study aimed at evaluating
the overall effects of fish oil supplementation in type II diabetics. Eleven subjects with non-insulin-
requiring type II diabetes took part in the randomized, double-blind, crossover study. All participants
underwent a 3-month run-in period during which they supplemented with olive oil capsules (placebo).
They were then randomized into two groups with one group supplementing with fish oil capsules (about
2.0 grams/day) and the other group supplementing with flax seed oil capsules. After 3 months the
participants underwent a crossover to the alternative oil for a final 3 months of supplementation.
All study participants had acceptable blood levels of total cholesterol, triglycerides, high density
lipoproteins, low density lipoproteins, and low density triglycerides prior to initiating supplementation with
fish oil or flax seed oil. Supplementation did not change these levels except in the case of triglycerides
which were markedly reduced after fish oil supplementation. Glycemic control was not adversely affected
by supplementation with either oil and there was a trend towards decreased insulin sensitivity in the group
taking fish oils. The researchers conclude that fish oil supplementation is safe in type II diabetes and can
help ameliorate cardiovascular disease risk factors such as high triglyceride levels. They also conclude
that flax seed oil supplementation, while having no adverse effects, is not of significant benefit in type II
diabetes. NOTE: This study was partially funded by the Canadian Dairy Bureau.
McManus, Ruth M., et al. A comparison of the effects of n-3 fatty acids from linseed oil and fish oil in
well-controlled type II diabetes. Diabetes Care, Vol. 19, May 1996, pp. 463-67
Fish oils recommended for diabetes and hypertension
TROMSO, NORWAY. Fish and fish oils help protect against the development of atherosclerosis and
heart disease. It is believed that fish oils exert their protective effect by lowering blood pressure and the
levels of triglycerides and very-low-density lipoprotein (VLDL). Fish oils are also believed to reduce
platelet aggregation and to suppress the growth of smooth-muscle cells in the arterial walls. Many people
with hypertension also suffer from diabetes and there has been concern that fish oil supplementation may
aggravate problems with glucose intolerance. Researchers at the University of Tromso now report that
fish oil supplementation lowers blood pressure significantly in people with hypertension and has no effect
on glucose control even in people with mild diabetes. The study involved 78 obese volunteers with
essential hypertension. The participants were randomly assigned to one of two equal-sized groups. The
fish oil group received four fish oil capsules a day (containing a total of 3.4 grams of a mixture of
eicosapentaenoic acid and docosahexaenoic acid) for a period of 16 weeks. The control group received
four corn oil capsules a day.
At the end of the test period the average (mean) systolic blood pressure had dropped by 4.4 mm Hg and
the diastolic pressure by 3.2 mm Hg in the fish oil group. The average blood pressure in the control
group did not change. The researchers also found that plasma triglyceride and VLDL levels in the fish oil
group decreased significantly (by about 9 per cent) while they increased significantly (by about 12 per
cent) in the control group. There were no changes in total or low-density-lipoprotein levels in either
group. Extensive tests (oral glucose tolerance, hyperglycemic and hyperinsulemic clamps) were done to
evaluate the effect of fish oil supplementation on glucose control. No adverse effects were found. An
editorial accompanying the research report concludes that fish or fish oil is useful in the prevention of
vascular disease in diabetics. Patients with diabetes should eat fish two to three times a week or, as an
alternative, supplement with two to three one gram capsules of fish oil per day.
Toft, Ingrid, et al. Effects of n-3 polyunsaturated fatty acids on glucose homeostasis and blood pressure
in essential hypertension. Annals of Internal Medicine, Vol. 123, No. 12, December 15, 1995, pp. 911-
18
Connor, William E. Diabetes, fish oil, and vascular disease. Annals of Internal Medicine, Vol. 123, No.
12, December 15, 1995, pp. 950-52
Fish oil supplementation recommended for type II diabetics
DALLAS, TEXAS. High cholesterol and triglyceride levels are common among diabetics and are major
contributors to their increased risk of cardiovascular disease. Researchers at the Texas Woman's
University and the University of Texas Medical Center now report that fish oil supplementation can
markedly decrease cholesterol and triglyceride levels without adversely affecting glycemic control.
Their study involved 40 patients with non-insulin-dependent diabetes mellitus (NIDDM) who had
abnormally high blood plasma levels of one or more of the following lipids: total cholesterol (greater than
5.17 mmol/L), LDL cholesterol (greater than 3.36 mmol/L), or triglycerides (greater than 6.47 mmol/L).
After a four-week baseline phase during which cholesterol levels, weight, blood pressure, and diabetes
control were assessed every two weeks the participants were randomly assigned to one of four groups -
daily dose of 9 grams of corn oil (57% linoleic acid), 18 grams of corn oil, 9 grams of fish oil (29% EPA
and 27% DHA), and 18 grams of fish oil. All participants were assessed every two weeks during the 12-
week supplementation period.
A significant reduction in the levels of very-low-density lipoproteins, triglycerides and very-low-density
triglycerides was observed among the participants supplementing with fish oils at both the 6-week and
12-week mark. There were no significant differences in the effect of 9 grams/day versus 18 grams/day
supplementation. The level of LDL cholesterol increased temporarily at the 6-week mark, but this effect
was no longer present at the 12-week examination. Neither fish oil nor corn oil supplementation
produced any significant changes (over baseline values) in total cholesterol levels, HDL cholesterol
levels, fasting plasma glucose, weight or blood pressure. A small increase in VLDL cholesterol was noted
in the corn oil group at the end of the experiment.
The researchers conclude that fish oil supplementation is useful in lowering triglycerides in diabetics with
excessive levels and has no deleterious effect on glycemic control.
Morgan, Wanda A., et al. A comparison of fish oil or corn oil supplements in hyperlipidemic subjects with
NIDDM. Diabetes Care, Vol. 18, January 1995, pp. 83-86
