Vitamin B1 deficiency explains bird population declines in northern Europe

Wild birds of several species are dying in large numbers from a paralytic disease with unknown cause near the Baltic Sea. A research team at Stockholm University, Sweden, led by Associate Professor Lennart Balk, has demonstrated strong relationships between this disease, breeding failure, and advanced thiamine (vitamin B1) deficiency in eggs, young, and adults.

In the living cell, thiamine's phosphorylated form acts as a cofactor for several life sustaining enzymes, which are useless without this cofactor. Thiamine is also necessary for proper nerve function. Thiamine deficiency was demonstrated in the egg, liver, and brain. Also, reduced thiamine concentrations in the liver and brain reduced activities of the thiamine-dependent enzymes. In the liver and brain, there were also elevated proportions of these enzymes without the thiamine cofactor.

Moreover, paralysed individuals were successfully remedied by thiamine treatment. The excess mortality and breeding failure are part of a thiamine deficiency syndrome, which most probably has contributed significantly to declines in many bird populations during the last decades.

The paralytic disease was observed in 78% of the investigated bird species (28 of 36). In some species, such as the herring gull, thiamine deficiency results in a reduction of the number of eggs. On the other hand, species like the common eider seem to be capable of producing eggs essentially devoid of thiamine. As a result, many herring gulls in the Baltic Sea area do not produce any eggs at all, and there is an excess mortality among common eider young.

The many observations of advanced thiamine deficiency strongly suggest that also a varying degree of moderate thiamine deficiency occurs among the affected species. One effect of moderate thiamine deficiency is altered behavior. The authors observed reduced aggressiveness and low noise level in herring gull colonies, as well as incomplete nest building in several species. Another effect of moderate thiamine deficiency is immune suppression. The avian influenza is just one example of a disease that may spread more easily among thiamine-deficient birds. Moreover, thiamine deficiency may weaken the blood-brain barrier, which normally protects the brain from many toxic substances.

Problem of excess mortality and breeding failure among birds has also received some attention previously, and has routinely been attributed to lack of food, but has now been shown to be caused by a thiamine deficiency that then causes a of loss of appetite and eventual starvation.

The thiamine deficiency may be induced either by a causative agent(s) acting directly on the affected individual, and/or by insufficient transfer of thiamine between the trophic levels in the food web. Classical persistent organic pollutants are not primarily suspected, since the affected species occupy a wide range of ecological niches and positions in the food web. Last but not least, the authors stress that they are open to the possibility that other wildlife may suffer from thiamine deficiency as well.

Source: Stockholm University