Vitamin D is known as the “sunshine Vitamin” because our body, like other animals, synthesizes D in reaction to sun exposure. Getting enough Vitamin D is essential to prevent Vitamin D deficiency diseases like rickets and osteomalacia, and recently researchers have discovered that higher levels of vitamin D may be beneficial in preventing a host of conditions, including fibromyalgia, rheumatoid arthritis, multiple sclerosis, upper respiratory tract infections, premenstrual syndrome, polycystic ovary disease, psoriasis, muscle weakness, lower back pain, diabetes, high blood pressure, cancer, and asthma.
Vitamin D is a critical factor in the regulation of nearly a thousand genes throughout the body. If those genes are not expressed properly, any number of issues can ensue, hence the wide-ranging health implications of Vitamin D deficiency. Conversely, increased levels of Vitamin D might even improve your mood and mental health.
Why is this particularly relevant for plant-based people? Other animals synthesize Vitamin D from the sun, just like humans, so people consuming animal products, like eggs or fish, are ingesting some amount of Vitamin D. Moreover, many dairy products are often fortified with vitamin D. Vitamin D intakes of vegans and vegetarians are generally lower than omnivores, and their serum concentrations are also lower, according to the EPIC Oxford and Adventist Health Studies. (If you want to know what your levels of Vitamin D are, you can get a blood test and make sure that your doctor measures “25(OH)D” or “25-Hydroxy vitamin D.” Remember that your levels are likely to be lower in winter than in summer.)
Like you, we are active and healthy people, and we love spending as much time outdoors as possible. But we also wear clothing and most of us have to work indoors. That means our natural ability to soak up the sun's rays is limited. This is particularly true for those of us living in the northern US, in Canada, or in northern Europe. Therefore, many of us — regardless of dietary pattern — are deficient in Vitamin D.
That’s why it’s critical for plant-based/vegans to ensure adequate (and safe) sun exposure, or to supplement with some form of Vitamin D. There are many plant-based sources that provide an algae- or mushroom-derived form of Vitamin D. And many plant-based milks (whether made from nuts or pea protein) are also fortified with Vitamin D, though this is usually vitamin D2. We suggest looking for D3 (cholecalciferol), which is the type synthesized by the human body and is the most biologically active form.