Hiperkalsemia, or excess calcium in the body, is a rare but very serious medical condition because it can cause damage to the bones, kidneys, and heart, as found in the autopsy of Mitchener. This excess occurs when too much vitamin D is consumed, which has become increasingly common post-Covid as people are promoting increased intake to boost the immune system.

Hiperkalsemia is a condition where there is an excessive accumulation of calcium in the body due to an excessively high amount of vitamin D. On May 10, 2023, Mitchener was admitted to East Surrey Hospital, but unfortunately passed away ten days later. Jonathan Stevens, an assistant coroner at the hospital, reported that the level of vitamin D in the man's body reached the maximum detectable level.

Before his death, tests showed that the vitamin D level in Mitchener's body reached 380 ng/mL, reaching the maximum point that could be detected by the laboratory. As an example, the Institute of Medicine (IOM) report in 2010 stated that a vitamin D level of 20 ng/mL is sufficient to maintain optimal bone health. Stevens, in his report on David Mitchener's death, highlights concerns that the use of vitamin supplements could pose potential risks and serious consequences if used excessively.