Is there a relation between Alzheimer's disease and sodium levels?

No, but can mimic. Low sodium levels can cause symptoms that mimic dementias like alzheimer's, and can worsen cognitive function in people who actually do have alzheimer's. Hyponatremia is a "treatable cause" of delirium -- or relatively acute onset of confusion, disorientation, memory dysfunction, etc associated with a medical cause. But it is not the same as alzheimer's disease.
No. Sodium levels.....Low or high doesnot cause alzheimers but such patients for various reasons can have abnormal values.