It’s not clear whether the TSH levels are causing or protecting against Alzheimer’s disease, or whether the Alzheimer’s is affecting TSH. The study was observational, and did not evaluate causality. It’s possible that pituitary responsiveness is damaged by Alzheimer’s disease, or that thyroid hormone irregularities may lead to Alzheimer’s.
Implications for Patients
While further study is needed, this study may end up providing additional reason for the medical community to finally adopt — universally and across the board — the narrower TSH reference range recommended more than five years ago.
Back in 2002, the American Association of Clinical Endocrinologists recommended narrowing the TSH reference range from the generally used 0.5 to 5.0 mIU/L, to a narrower range of 0.3 to 3.0, with the National Association of Clinical Biochemistry recommending an even lower top limit of 2.5. While some doctors and endocrinologists have adopted the new recommendations, the TSH range issue is controversial, and laboratories are still evaluating thyroid blood tests according to the old 0.5 to 5.0 range.
In the meantime, however, this study provides further evidence to argue that, for patients receiving thyroid treatment, the target range for optimal TSH should be between 1.0 to 2.0, unless other more immediate factors are involved. (For example, some thyroid cancer patients are maintained on suppressive doses of thyroid medication, keeping TSH low — and sometimes near 0 — to prevent cancer recurrence.)