There are several proposed mechanisms by which hypovitaminosis D may impact these disorders.

Hypovitaminosis D has been associated with many neurological conditions.

One 2008 review has proposed the following four categories for hypovitaminosis D:

Hypovitaminosis D is also considered a risk factor for the development of depressive symptoms in older persons.

In the past, hypovitaminosis D has been defined by blood concentrations lower than 20 ng/ mL.

In recent studies, several associations between low levels of vitamin D, or hypovitaminosis D, and neuropsychiatric disorders have begun to surface.

Risk factors for hypovitaminosis D include premature birth, darker skin pigmentation, living at higher altitudes, obesity, malabsoprtion and older age.

Surgical reduction of sites in the terminal ileum for active and exclusive uptake of vitamin B12 might lead to hypovitaminosis.

Hypovitaminosis D is associated with an increase in pro-inflammatory cytokines and decrease in anti-inflammatory cytokines.

Hypovitaminosis D is associated with several neuropsychiatric disorders including dementia, Parkinson's disease, multiple sclerosis, epilepsy, and schizophrenia.

Hypovitaminosis D causes this specific apoptosis by decreasing the expression of cytochrome C and decreasing the cell cycle of neurons.

Adjunctive symptoms, such as cheilitis, glossitis, blepharitis, night blindness, diarrhea, muscle weakness and neuritis, may develop when hypovitaminosis A is predominant relative to other vitamin deficiencies.

This clothing when worn on a consistent and regular basis, such as the burqa, is correlated with lower vitamin D levels and an increased prevalence of hypovitaminosis D.

Hypovitaminosis D is typically diagnosed by measuring the concentration in blood of the compound 25-hydroxyvitamin D (calcidiol), which is a precursor to the active form 1,25-dihydroxyvitamin D (calcitriol).

Megaloblastic anemia not due to hypovitaminosis may be caused by antimetabolites that poison DNA production directly, such as some chemotherapeutic or antimicrobial agents (for example azathioprine or trimethoprim).

Hypovitaminosis A (also known as Follicular Hyperkeratosis and "Phrynoderma" which means Toad Skin) is common in children in the developing world, most often associated with diseases of fat malabsorption.

Hypovitaminosis D is described as any deficiency of vitamin D. A vitamin D blood concentration standard for diagnosing hypovitaminosis D does not exist.

Xerophthalmia from hypovitaminosis A is specifically due to lack of the hormone-like vitamin A metabolite retinoic acid, since (along with certain growth-stunting effects) the condition can be reversed in vitamin A deficient rats by retinoic acid supplementation (however the retinal damage continues).