Vitamin D, cod liver oil protect against diabetes
on in life appear to reduce the risk of type 1 diabetes, suggests
new trials out this month. But neither study finds a positive
effect from supplements.
In the first study a team from the University of Colorado Health Science Center in Denver, US found an association between a mother's intake of vitamin D during pregnancy and reduced risk of diabetes for her offspring.
The team, reporting in this month's Diabetes Care (26:3237-3242), examined the impact of vitamin D, omega-3 fatty acids and omega-6 fatty acids during pregnancy on the appearance of islet autoimmunity in offspring. Type 1 diabetes can occur when the islet cells in the pancreas that produce insulin are knocked out by an autoimmune reaction.
More than 230 mothers of children recently recruited to the Diabetes Autoimmunity Study in the Young (DAISY), which is following children at increased risk for type 1 diabetes, were asked to recall their intake of food and nutritional supplements during the third trimester of pregnancy using a food frequency questionnaire.
Children were followed for an average of four years for the appearance of insulin, as well as GAD65 and IA-2 autoantibodies. Sixteen children developed at least one autoantibody during this period.
The team found that maternal intake of vitamin D from food was significantly associated with a decreased risk of islet autoimmunity in offspring, independent of other risk factors. Mothers with affected children had an average daily vitamin D intake in food of 167.6 units, while the group with unaffected children had an average intake of 252.3 units.
But vitamin D intake from supplements, omega-3 fatty acids and omega-6 fatty acids were not associated with risk of diabetes in offspring.
Some of these findings are confirmed in the second study, reported in December's American Journal of Clinical Nutrition(vol 78, no 6, 1128-1134).
An Oslo team investigated whether the use of dietary cod liver oil or other vitamin D supplements, either by the mother during pregnancy or by the child during the first year of life, is associated with a lower risk of type 1 diabetes among children.
They selected 545 cases of childhood-onset type 1 diabetes and 1668 population control subjects for the nationwide case-control study. Families completed a questionnaire on the frequency of use of cod liver oil and other vitamin D supplements.
Use of cod liver oil in the first year of life was associated with a significantly lower risk of type 1 diabetes but use of other vitamin D supplements during the first year of life and maternal use of cod liver oil or other vitamin D supplements during pregnancy were not associated with type 1 diabetes.
The researchers suggest that cod liver oil may reduce the risk of diabetes through the anti-inflammatory effects of omega-3 fatty acids.However neither team could explain why vitamin D supplements had no effect. It could be related to different absorption of vitamin D from supplements.
Diabetes is the fourth main cause of death in most developed countries, according to the International Diabetes Federation, and it is the leading cause of blindness and visual impairment in adults in developed countries.
