Vitamin D: loooves fatty foods, sunshine, and hates being sick. You too? You definitely need more vitamin D in your life. In fact, according to a Harvard study, more than a billion people worldwide could use more vitamin D in their lives.

Despite its popular moniker, vitamin D isn’t actually a vitamin, but actually a hormone produced in the skin after exposure to sunlight. Since “Hormone D” sounds pretty weird, we’ll stick to VD. (OK that’s even worse – vitamin D it is!). Typically, vitamins cannot be produced by the body so you need to get them from food sources or supplements, but vitamin D is made in the body.

So, what does Vitamin D do?
Vitamin D is essential for the absorption of dietary calcium in the body. Plus, says Dr. Leo Galland, one of the most renowned integrative medicine doctors in the world and one of the founders of functional medicine, “Vitamin D also has profound effects on immune function. It is both anti-inflammatory and anti-viral and helps to prevent cancer.”

While vitamin D deficiency was originally identified as the cause of rickets, a bone disease in children, today’s research continues to prove just how important this hormone is for our health and well-being. Recent studies show the relationship between vitamin D deficiency and cognitive decline, depression, digestive problems, osteoporosis, heart disease, some cancers, MS, tuberculosis and even the seasonal flu.

Do I need more D?
Suddenly everyone – from your best friend to Gwyneth Paltrow – is supposedly deficient in this ubiquitous nutrient. So, why the sudden obsession with Vitamin D and why do we all need it?

Galland blames your TV set. “Since the growth of television in the 1950’s, people have been spending more and more time indoors, and since the 1980’s there has been increasing use of sunblock outdoors to prevent skin cancer, so it is likely that vitamin D levels have been dropping.” Plus, the optimal blood level of vitamin D is actually higher than doctors previously thought. We don’t necessarily have less, we just need more.

Vitamin D is present in many foods, but according to Galland these foods “do not supply enough vitamin D to overcome our dependence on the sun. To be active in our bodies, vitamin D must be converted in the liver to a derivative called 25-hydroxy-vitamin D, which is then converted to the active hormone called calcitriol in the kidneys and cells of the immune system.” In sum, you can’t have your vitamin D and eat it too.

Foods like cod liver oil and the flesh of fatty fish like salmon, mackerel, sardines and tuna contain the highest levels, but, says Galland “It is hard to obtain adequate levels from food alone. Oily fish would need to be eaten daily. In the case of tuna, there would be excessive consumption of mercury for this to be a safe alternative.” Other plant-based sources include almonds, tofu, chanterelle mushrooms and fortified soy and almond milks.

How do I pick a supplement?
Unless you want to abide by the adage, “A pound of oily fish per day keeps the doctor away,” you may want to stick to supplements.

Galland recommends vitamin D3, a form called cholecalfierol that is directly converted in the liver to 25-hydroxy vitamin D. The optimal dose varies from person to person, so get tested to see where your levels are. Some doctors will test your vitamin D level at your annual physical, but if yours doesn’t, just ask! Plus, keep in mind that blood levels of D can vary depending on the season and tend to be lowest in winter and higher in warmer months. A blood level of 30 ng/mL (nanograms per milliliter) was originally considered optimal, but now many health experts argue that we need more like 40-50 ng/mL.

One last word of warning: be careful not to OD on VD. Says Galland: “Because vitamin D is fat soluble, it is stored in the body’s cells, especially fat cells. Excessive consumption can lead to blood and tissue levels that are too high. The best studied side effect of vitamin D toxicity is elevated calcium concentration in blood and urine, which can cause formation of kidney stones.”

Rebecca Leffler is an American journalist, author, and wellness consultant. After a long career in entertainment in Paris, France, she’s traded red carpets for green smoothies and croissants for kale. She loves: the morning, yoga, avocados, fresh air, French air, puns, lemons, coconuts, flower, fancy hotel lobbies and chemical-free tampons. She hates: pineapples, negativity, frowning and being cold. Follow her on Instagram or Twitter for more. Photo credit: Astrid di Crollalanza.

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