Cod Liver Oil ranks among some of the safest nutritional supplements primarily because it is essentially a food. In a normal diet of moderate seafood intake people are exposed to doses of omega 3 fatty acids like those found in cod liver oil supplements.
These essential fatty acids are a primary component of health and due to the fact that people do not eat foods rich in Omega 3 fatty acids I feel it is of utmost importance that they be supplemented with a good source such as that from cod liver oil.
Omega 3 fatty acids play a crucial role in brain and neurological function so it is particularly important at times when the neurological system needs more support like during development and when we are older. Appropriate intake of omega 3 fatty acids has been correlated to enhanced mental function in older individuals.
We also know that omega 3 fatty acids support the heart and cardiovascular system. To answer you question regarding the diabetes, cod liver oil can help to support the health of the blood vessels which are subject to excessive stress in people with diabetes.
The only major warning in regards to taking cod liver oil, or any fish oil for that matter, is its potentially mild blood thinning effects. Fish oils tend to make the cells in our body that are responsible for clotting slightly more slippery. This can create problems for people with bleeding disorders, or more commonly for those people taking anti-coagulant therapy such as Warfarin, Coumadin or Plavix. You will want to discuss the possibility of taking fish oil with your doctor first if you are taking any of the above mentioned medications. Otherwise, there is very little evidence suggesting that cod liver oil can interfere with or alter the activity of other medications.