There is a lot of literature and a fair amount of research about the link between vitamin D deficiency and insomnia. But in the case of the opposite phenomenon of a standard or excessive daily dose of the "sunshine vitamin" impairing a person's ability to sleep, the evidence is much more grassroots and, thus, somewhat inconclusive.
For example, testimonials from vitamin D supplement takers left in one diet community online forum support the exact opposite idea that rather than cause insomnia, vitamin D can help cure it. A woman explained that adding D3 supplements to her daily, healthier diet regimen led to a major improvement in her sleep patterns.
In 2009, in order to get over a sinus infection, a male patient in his mid-40s took large daily doses of vitamin D supplements for a period of nine months. Among the symptoms he experienced were insomnia, showing once again that, yes, it can lead to this problem.
A doctor reviewing the details of his case judged that this man's testimony amounted to one of the first modern-age documented cases of a person making themselves toxic by taking too large a regular quantity of the vitamin. Complicating this situation is the fact that the male patient's five-year-old daughter was also taking vitamin D dosage.
Luckily, such a toxicity is easily treatable, provided it has not caused permanent damage to vital organs. By stopping the intake of vitamin D, drinking lots of water, and having blood work done to ensure that the kidneys are functioning properly, patients such as this pair can leave insomnia and larger issues behind.