Key messages

• Very few clinical trials have evaluated the benefits and harms of omega-3 fatty acid supplements for treating peripheral nerve damage (damage to nerves outside the brain and spinal cord) associated with diabetes.

• Larger, well‐designed studies are still needed to understand whether omega‐3 fatty acid supplements can reduce the risk of developing impairments, such as loss of normal function or ability, and symptoms associated with nerve damage in people with diabetes.

• There may be little or no difference between omega‐3 fatty acid supplements and placebo (‘dummy’ treatment) in the occurrence of unwanted side effects among people with diabetes, when the treatment is taken over the course of six months, but we are very uncertain about the results.

What is diffuse distal symmetrical polyneuropathy?

Diffuse distal symmetrical polyneuropathy is a nerve disorder that can occur in people with diabetes. It affects the nerves that carry sensation and the nerves that control muscle movements. Common symptoms include tingling, burning, numbness, and pain in the hands and feet. People with this condition can also experience muscle weakness, loss of reflexes, sores or ulcers on the feet that do not heal well, or loss of sensation in the hands and feet, which can affect co-ordination and walking.

How is diffuse distal symmetrical polyneuropathy treated?

Diffuse distal symmetrical polyneuropathy is currently treated by managing symptoms, such as pain, and preventing further nerve damage, by controlling blood sugar levels through diet, exercise, and diabetes medications. There are currently no treatments that can effectively prevent, reverse, or cure the nerve damage itself.

What did we want to find out?

We wanted to find out if oral omega-3 supplements were better than placebo treatment or no treatment to improve impairment and symptoms associated with nerve damage in diabetes.

What did we do?

We searched for clinical trials that looked at omega-3 supplements, compared to placebo or no treatments, in adults with diabetes with diffuse distal symmetrical polyneuropathy. We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as the study methods and sizes.

What did we find?

We found two studies that, together, involved 87 people with type 1 and type 2 diabetes, who received either omega-3 supplements or placebo treatment for six months.

Compared with placebo treatment, omega-3 fatty acid supplements taken for six months may make little or no difference to peripheral neuropathy impairment, symptoms of peripheral neuropathy, or well-being. Although not a main outcome of this review, it is possible that omega-3 supplements might improve nerve health in the cornea (the clear front part of the eye) compared to placebo supplements. However, these findings are based on results from a single clinical trial, as the second trial did not study this outcome. As a result, we are uncertain about whether these findings are generalisable to all people with diabetes or how clinically meaningful any benefits may be.

Omega-3 fatty acid supplements may not cause any more unwanted effects compared to placebo treatment, but we are very uncertain about the results.

What are the limitations of the evidence?

We have low confidence in the evidence as only two clinical trials evaluated the benefits and harms of omega-3 supplementation for treating nerve damage in adults with diabetes, and both studies involved only a small number of people. Only one of the two studies was available as a scientific publication, and it was the only study that provided data about the effectiveness measures that we were interested in. Further evidence may well change these results.

How up to date is this evidence?

The evidence is up to date to June 2024.