High serum omega-6 polyunsaturated fatty-acid (PUFA) levels are associated with a significantly reduced risk of type 2 diabetes, new research suggests.
The findings, from an analysis of more than 2000 men participating in the Kuopio Ischaemic Heart Disease (KIHD) Risk Factor Study, were published online March 24 in the American Journal of Clinical Nutrition by Jyrki Virtanen, PhD, adjunct professor of nutritional epidemiology at the Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, and colleagues.
In the body, linoleic acid (LA) is converted to other n–6 PUFAs: gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA), and arachidonic acid (AA). These fatty acids can also be obtained from the diet in minor amounts, and AA is derived especially from animal products, but their concentrations in the body mainly reflect endogenous formation from linoleic acid.
The analysis showed that serum linoleic acid and arachidonic acid were associated with a lower type 2 diabetes risk, and GLA and DGLA with a higher risk.
"Linoleic acid is an essential fatty acid, so it is not formed in the body and must be obtained from diet. Therefore, the blood levels of linoleic acid reflect dietary intakes. The best sources of linoleic acid are vegetable oils, nuts, and seeds, so these food items could be beneficial in the prevention of type 2 diabetes," Dr Virtanen told Medscape Medical News. However, he added that intake of nuts and seeds were very low in the KIHD study, so the main sources for the cohort were vegetable oils and margarines.
Although the levels of arachidonic acid are determined partly by conversion from linoleic acid in the body, arachidonic acid can also be obtained from diet. "One of the best sources is eggs, and we have previously shown in this KIHD population that higher egg intake was associated with lower risk of type 2 diabetes," he noted (Am J Clin Nutr. 2015;101:1088-1096).
The study also identified a major role for zinc, an essential cofactor for the delta-5- and delta-6-desaturase enzymes that are involved in PUFA metabolism: The higher diabetes risk with higher serum GLA concentration was found only among those with a higher serum zinc concentration. Similarly, the lower risk with a higher serum arachidonic acid concentration was observed only among those with lower serum zinc concentrations.
That, combined with the previous KIHD finding that higher serum zinc concentration was associated with a higher risk of type 2 diabetes, suggests that zinc may have a role in determining the impact of the n-6 polyunsaturated fatty acids on the risk of type 2 diabetes, he noted.
However, he said, "It is difficult to give any practical dietary advice based on these findings, because serum zinc concentrations are quite strictly regulated, so normal dietary intakes have a very modest impact on serum zinc concentrations."
Fatty Acids and Diabetes Risk
In the study of 2189 men aged 42 to 60 at baseline and followed for an average 19 years, those in the highest compared with the lowest quartile of serum total n–6 PUFAs had a 60% lower risk for incident type 2 diabetes after adjustment for age and examination year (P for trend across quartiles < .001). The risk attenuated slightly after adjustment for confounders but remained highly significant.
When fatty acids were evaluated individually, serum linoleic acid and arachidonic acid had similar inverse associations with the risk of type 2 diabetes. With full adjustments, those in the highest compared with the lowest serum LA quartile had a 48% lower risk (P for trend < .001), while the highest vs lowest AA quartiles showed a 38% reduced risk (P for trend = .007).
In contrast, higher serum GLA and DGLA concentrations were associated with a higher type 2 diabetes risk, by 28% for the highest vs lowest GLA quartile ( P for trend = .021) and 38% greater risk for the highest vs lowest DGLA quartiles (P for trend = .005).
"There are very few dietary sources of GLA and DGLA, so their blood levels mainly reflect conversion from linoleic acid in the body. It is not very clear why they are associated with a higher risk in our study and also in some previous studies. However, the blood levels of GLA and DGLA are very low, and in our study total n-6 PUFA levels were associated with a significantly lower risk of type 2 diabetes. So the impact of GLA and DGLA on the risk may not be that significant," Dr Virtanen commented.
In secondary analysis, serum GLA was associated with a higher risk of type 2 diabetes only among the men with serum zinc above the median (P for trend = .002, P interaction = .041). In contrast, although the P interaction did not reach significance (P = 0.11), an inverse association between AA and type 2 diabetes risk was observed only among those with lower serum zinc concentrations (hazard ratio, 0.45; P for trend = .001).
All of these findings should be regarded as preliminary and require further research, especially in other study populations, he concluded.
The authors have no relevant financial relationships.
Omega-6 PUFAs in Diet Seem to Cut Diabetes Risk Medscape. Mar 30, 2016.