The Surprising Health Problems from Not Enough Vitamin D
Learn the surprising ways that vitamin D supports our health, how much we actually need, and the best food sources.
Introduction
Despite its name, vitamin D is actually a group of fat-soluble steroid hormones rather than a true vitamin (since vitamins are defined as nutrients that must be obtained from food and can’t be synthesized by the body, which isn’t the case for vitamin D!). In humans, the most important forms are vitamin D3 (also called cholecalciferol) and vitamin D2 (also called ergocalciferol).
Fascinatingly, vitamin D is believed to be the oldest hormone on earth—having existed for at least 750 million years, when phytoplankton in the ocean began producing it in reaction to sunlight exposure. Although we don’t know exactly why it first developed, it’s likely that vitamin D helped in the evolutionary transition from water to land by allowing organisms to utilize calcium and develop skeletons.
As with some other vitamins (like vitamin A, vitamin B1, and vitamin C), the discovery of vitamin D ultimately came about from trying to cure its deficiency disease! Medical writings from the early Romans and Greeks describe the bone condition we now call rickets (caused by vitamin D deficiency), and when the Industrial Revolution arrived, rickets became more and more widespread due to dietary changes and people spending increasingly less time outdoors. For centuries, physicians tried to find a cure for this mysterious disease, with attempts ranging from painful failures (such as cauterizing veins) to successes (prescribing cod liver oil). Vitamin D was finally identified as the “fourth vitamin” in 1919, and named vitamin D a few years later (owing to the custom of naming vitamins in alphabetical order, with vitamin D following C). It took many more decades before scientists began understanding its metabolism and role in maintaining calcium and phosphate levels.
Vitamin D is important for the intestinal uptake of several other nutrients (including calcium, magnesium, and phosphorus); it’s also essential for cellular differentiation, bone density, immune function, endocrine health, and cardiovascular health.
Food sources of vitamin D include fatty fish (like salmon, mackerel, sardines, and herring), fish eggs (roe), liver, red meat, and egg yolks. Mushrooms grown under UV exposure are the only substantial non-animal-food source of naturally occurring vitamin D (mostly in the form of vitamin D2); grown under the same conditions, baker’s yeast can also produce vitamin D2. And, in some countries (including the US), a number of foods that don’t naturally contain vitamin D are fortified with it, such as store-bought orange juice, cereals, some dairy products, and plant-based milks.
This article explains the biological roles of vitamin D, the interactions between dietary vitamin D and our risk of 10 categories of health problems (encompassing more than two dozen health conditions), symptoms and signs that our levels of vitamin D are too low, how much vitamin D we need by demographic (and how much is too much), and shares the top 25 best common food sources of vitamin D.
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The Biological Roles of Vitamin D
