Our findings suggest that age dependent prolonged P300 latency, as well as age dependent increased PTH levels, may interact. This is a timely discovery since there has been a recent influx of research highlighting the connections between the brain and the bones, and a new field has been birthed called neuropsychosteology [21, 22]. Many studies have confirmed neuropsychiatric disease increases with osteoporosis (OP) [23–25].
Our measurement of PTH did not take into account factors that could affect analysis: age, gender, menopausal status, vitamin D and calcium supplementation, smoking, alcohol consumption, steroid use, family history of osteoporosis, physical activity, drugs to control bone and calcium metabolism, rheumatoid arthritis, other diseases that cause secondary osteoporosis, levels of sex hormones, etc. Further studies will be needed to clarify all of these variables in relation to PTH's effects on the aging brain and aging skeleton.
Based on our findings, we suggest that control of PTH levels may be important for protecting against age-induced dementia. PTH's potential involvement with dementia may be explained in the following way: PTH has been shown to cross the blood-brain barrier . PTH has been considered a candidate risk factor for senile dementia because sustained high levels of PTH in the brain may cause degeneration of specific brain regions due to Ca(2+) overloading [27, 28].
Moreover, OP is a genetic disease and as such the role of 1,25-dihydroxyvitamin D3-receptor gene polymorphisms, known OP genetic antecedents  may contribute in some way to the age-linked impairments in both parathyroid and neurological processing function. It is to be noted that PTH tides are of short duration while Vitamin D or calcitriol tides are of long duration. PTH quickly mobilizes bone calcium, while calcitriol tends to more slowly increase the absorption of dietary calcium. In the case of low or no dietary calcium, calcitriol mobilizes bone calcium together with PTH. Because of this, mixed effects occur during Vitamin D deficiency, and pseudo- or secondary hyperparathyroid conditions occur. Furthermore, overnight fasting with reduced absorption of dietary calcium associated with age results in a regulatory set point inducing an increase of PTH secretion with age.
It is apparent that PTH levels should be kept below 60 pg/ml, and we believe based on our findings that these levels may be lowered still. Further research should involve P300 latency testing for a larger number of patients and stratification by age, and correlating PTH levels and BMD. This study provides the first potential indirect evidence that may highlight the importance of processing speed as an early electrophysiological marker of OP, which warrants further investigation.
Increases in PTH levels with age are major factors responsible for age-related increase in bone resorption, and contribute to kidney stone formation as well . PTH levels need to be monitored in osteoporotic, memory-impaired people and lowering the levels may be an important part of the therapeutic process of teriparatide injections. At the PATH Medical Clinic, PTH levels were reduced by teriparatide injections by an average of 20 points, possibly due to a negative feedback mechanism. This is further supported by others . Additional research has shown that teriparatide therapy may need to be supplemented by GH or GH-dependent factors in order for the anabolic response of bone [32, 33].
Finally, the findings of this study showing a significant relationship between higher PTH plasma levels and prolonged P300 latency as well as a decrease in BMD suggest that hyperparathyroidism and elevated PTH due in part to age may lead to dementia and OP. The connection between elevated PTH and cognitive decline is becoming well studied. A recent study published in the Journal of Clinical Endocrinology and Metabolism presented results of various cognitive testing in postmenopausal women with hyperparathyroidism, before and after parathyroidectomy, with pre-surgical cognitive impairments improving after surgery . Further studies are warranted to confirm the value of increased PTH levels coupled with increased P300 latency as putative biological markers of both dementia and OP.