The study said that vitamin D levels above 100nmol/L were associated with higher risk from CVD and stroke. I don't have access to the study so I don't know what the mortality was from in the low ranges. Presumably, the higher than optimal vitamin D levels probably caused arterial calcification, and the lower ones increased PTH. The study abstract says both calcium and PTH were factors influencing all-cause mortality. Since low calcium was also associated with mortality, I suspect this is due to kidney disease as it is the main cause of low serum calcium.
http://www.sciencedaily.com/releases/20 ... 105222.htm
http://www.ncbi.nlm.nih.gov/pubmed/22573406
http://www.ncbi.nlm.nih.gov/pubmed/25710567
"...RESULTS: During follow-up (median, 3.07 yr), 15,198 (6.1%) subjects died. A reverse J-shaped association between serum level of 25(OH)D and mortality was observed. A serum 25(OH)D level of 50-60 nmol/liter was associated with the lowest mortality risk. Compared to 50 nmol/liter, the hazard ratios (95% confidence intervals) of all-cause mortality at very low (10 nmol/liter) and high (140 nmol/liter) serum levels of 25(OH)D were 2.13 (2.02-2.24) and 1.42 (1.31-1.53), respectively. Similarly, both high and low levels of albumin-adjusted serum calcium and serum PTH were associated with an increased mortality, and secondary hyperparathyroidism was associated with higher mortality (P < 0.0001)."
http://www.sciencedaily.com/releases/20 ... 105222.htm
http://www.ncbi.nlm.nih.gov/pubmed/22573406
http://www.ncbi.nlm.nih.gov/pubmed/25710567
"...RESULTS: During follow-up (median, 3.07 yr), 15,198 (6.1%) subjects died. A reverse J-shaped association between serum level of 25(OH)D and mortality was observed. A serum 25(OH)D level of 50-60 nmol/liter was associated with the lowest mortality risk. Compared to 50 nmol/liter, the hazard ratios (95% confidence intervals) of all-cause mortality at very low (10 nmol/liter) and high (140 nmol/liter) serum levels of 25(OH)D were 2.13 (2.02-2.24) and 1.42 (1.31-1.53), respectively. Similarly, both high and low levels of albumin-adjusted serum calcium and serum PTH were associated with an increased mortality, and secondary hyperparathyroidism was associated with higher mortality (P < 0.0001)."