I am wondering if people find that their sleep improves after they spend time in the summer sun. It may take until the end of the summer until the vitamin D rise to a high enough level to make a difference.
https://www.texassleepsolutions.com/wp-content/uploads/2016/Sleep-disorders-linked-to-Vit D.pdf (2012)
abstract
An observation of sleep improvement with vitamin D supplementation led to a 2 year uncontrolled trial of vitamin D supplementation in 1500 patients with neurologic complaints who also had evidence of abnormal sleep. Most patients had improvement in neurologic symptoms and sleep but only through maintaining a narrow range of 25(OH) vitamin D3 blood levels of 60–80 ng/ml. Comparisons of brain regions associated with sleep–wake regulation and vitamin D target neurons in the diencephalon and several brainstem nuclei suggest direct central effects of vitamin D on sleep. We propose the hypothesis that sleep disorders have become epidemic because of widespread vitamin D deficiency. The therapeutic effects together with the anatomic–functional correspondence warrant further investigation and consideration of vitamin D in the etiology and therapy of sleep disorders.