Table 3.
Summary of findings.
| Outcome of interest | Studies (N) with ‘U’-shaped findings, by topic | Type of study | Reference | Validity | Comments | Possible Non-causal confounders Identified |
|---|---|---|---|---|---|---|
| Allergies | Probable | Common findings | Shift of Th cell balance from Th1 to Th2 cells, increasing inflammatory cytokines | |||
| Cancer, of the prostate | 6 | NCCMeta-analysis | 21,23,24,26,28 | Probably not | Confounding by PSA testing possible | Unknown |
| Pancreatic Cancer | 2 | NCC | 16,17 | No | Not found at lower latitudes | Possible recent high-dose vitamin D supplementation (before blood draw) |
| CVD | 3 | Prospective | 43-45,111 | Probably not | U-shaped relationship found in 3studies; 1,25(OH)2D measured in one study. Not found in most studies. | Recent vitamin D supplementation, meat consumption, low 1,25(OH)2D production |
| Cognition | 3 | 80-82 | No | Weak studies, not consistent in outcomes | Recent vitamin D supplementation | |
| Falls, fractures, bolus doses | 2 | 67,72 | Maybe | Repeated | ||
| Fractures | 1 | Prospective | 73 | No | Recent vitamin D supplementation | |
| Frailty status | 1 | Cross-sectional | 50 | No | Observed for women but not men | Recent vitamin D supplementation |
| Mortality rate | 3 | 40,86,88 | Probably not | Observed in some studies; found for some outcomes | CVD, PC. | |
| Pregnancy outcomes | 2 | 90,92 | No | Found in only 2 studies | Not known, but 25(OH)D was measured at <22 weeks' gestation or at term at a single time point Data on dietary intake (vitamins A, C, K; calcium; and magnesium) not available |
NCC, nested case–control