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Vitamin D for immunity? Additional info and a great graphic

Editor’s Note: Marion Nestle, Ph.D (molecular biology), and emeritus professor of nutrition at New York University writes one of my favorite blogs, “Food Politics.” In my recent column about immunity and vitamin D, I explained that it is necessary to obtain sufficient vitamin D from food and from sunshine — vitamin D is essential for a healthy immune system, especially important in this time of Covid-19. In her recent blog post, Dr. Nestle succinctly explains how the body manufactures vitamin D. Read her May 26 column, “Vitamin D and Coronavirus? Will it help?” 

By Marion Nestle
I wrote about current research suggesting that higher levels of blood Vitamin D [actually, 25-hydroxycholecalciferol, or 25(OH)D] help to protect against Covid-19.

To understand concerns that this evidence may not be totally convincing, it’s useful to know the basics about this “vitamin,” which I put in quotes because its active form is a hormone that helps govern calcium balance.  Here’s how it works.

  • Sunlight acts on a form of cholesterol in skin (7-dehydrocholesterol) to covert it to cholecalciferol, the chemical name for vitamin D3.
  • Vitamin D3 goes to the liver where an enzyme converts it to 25 (OH)D.
  • 25(OH)D goes to the kidney where an enzyme converts it to 1,25-dihydroxycholecalciferol (a.k.a. 1,25-dihydroxyvitamin D), the active hormone.

If you eat foods containing vitamin D3 (fish and meat, which have it in very small amounts, or fortified milk) or vitamin D2 from plants, yeast, or supplements, these travel in the blood to the liver where they undergo the same metabolic steps.

This means that there are three sources.

  • Sunlight on skin—this produces thousands of IU (International Units)
  • Food—is low in this vitamin
  • Supplements—vary, but high doses are not recommended by most health authorities; they may induce hyper-immune responses (not a good idea)

The commonly recommended daily dose of vitamin D is 400-600 IU.

Sunlight on skin is by far the best way to get your vitamin D hormone.

Sensible sun exposure, especially between the hours of 10:00 am and 3:00 pm produces vitamin D in the skin that may last twice as long in the blood compared with ingested vitamin D.If sun exposure produces slight pinkness, the amount of vitamin D produced in response to exposure of the full body is equivalent to ingesting 10,000-25,000 IU.

 In the UK, a study showed that 13 minutes of midday sunlight exposure during summer, just three times per week, maintains healthy levels in white adults ; other studies have shown 30 minutes of midday summer sun exposure in Oslo to be equivalent to consuming 10,000–20,000 IU of vitamin D.

How does all this relate to Covid-19?

So far, we do not have studies of vitamin D supplements in patients with Covid-19 or longer term prospective trials.  These will undoubtedly come.

While waiting for those results, enjoy the sunshine!

Marion Nestle is Paulette Goddard Professor, of Nutrition, Food Studies, and Public Health, Emerita, at New York University, which she chaired from 1988-2003 and from which she officially retired in September 2017.

Credit: Bill Haye

She is also Visiting Professor of Nutritional Sciences at Cornell.  She earned a Ph.D. in molecular biology and an M.P.H. in public health nutrition from the University of California, Berkeley, and has been awarded honorary degrees from Transylvania University in Kentucky (2012) and from the City University of New York’s Macaulay Honors College (2016).



18 thoughts on “Vitamin D for immunity? Additional info and a great graphic

    1. Great question. I have wondered the same. I would say “yes”since you can turn pink in about a half hour of exposure.
      I have been catching 20 minutes every other day (when it is not raining) and I get slight color from that. Much more and I get red and itchy. The sun can be unbelievably hot here. If it is partly cloudy I go ahead and increase the time to about 30 minutes. I am sure everyone’s exposure needs varies.

    2. It’s possible to get a sunburn on a cloudy day if you’re out long enough. My guess would be yes.

    3. good question – from the NY Times: “Just as it is possible to get a sunburn on an overcast day, it is possible to get the ultraviolet-B radiation needed for the skin to synthesize vitamin D even when skies are cloudy and gray. Efficiency varies, however, with the season, the altitude, skin color, the length of skin exposure and the percentage exposed, and air pollution.”
      More on how much you need if you can’t get sunshine – my column

    4. Hey, Pix, yes you can. Some sunlight is better than none. Plus, that’s why God put the pituitary and hypothalamus glands right behind the eyes- they function best in full-spectrum sunlight. They handle dozens of needed tasks. Without sunglasses/sunscreen (cancerous). They function decently on cloudy days, also. Richie T. knows this, too.

      1. Hiram, I have a couple of those glands but I keep them out of the sun for the most part. (:

          1. Come on Anthony. I thought that was kind of amusing. No, I’m not easily amused. We CAN disagree without always being disagreeable. We ALL need to lighten up.

    5. It would nice if there was a subcutaneous chip they could implant to monitor such things. Of course you can have a blood test to check that. I wonder what it costs. I had a cholesterol test (just the total amount not knowing they wouldn’t break down the type) for $2.50 a few months back in Otavalo. Could be cheap…..

      1. vit d (OH) typically runs around $35 at the Mt Sinai level. Wholistic practitioners recommend you keep your levels between 50 ng/ml and 80 ng/ml (mid range depending on the test parameters). It has been demonstrated in countless studies that keeping your levels above 30 ng/ml is helpful against cancers and countless other illnesses—or rather that people who have those illness seem to all have vit d levels below 30 ng/ml. the dosages this writer lists are way to low in the majority of cases to keep peoples levels above 30 however as she notes it needs to be regularly monitored so it is not too high. work with your practitioner regarding dosage and monitoring.

        1. It seems to me that prices of lab work can vary quite a bit depending on the lab or city you are in. I paid $35 in 2018 in La Libertad for a blood and urine test that measured a whole host of things. It was a standardized exam that was intended for routine medical checkups.

        1. Can you recommend an inexpensive lab for me in Cuenca? In the past I had blood tests in other cities. Thanks.

          1. Dear Swami,
            You need to know that compared to the USA the costs here are quite low. I use Laboratorio Clinico Interlab on Honoratio Loyola and Frederico Proano. Tel#04-259 4010 ext.325.

  1. There is a very well documented increased incidence of poor bone healing after surgery, especially regarding bone fusions, in patients with low levels of vitamin D. We used to routinely test it preoperatively in patients undergoing fusions in foot surgery, and in patients with fractures notorious for poor healing, and supplement until levels were within normal limits. And why would you suspect that there were so many patients in Texas with low vitamin D levels? This is actually more common in hotter climates because people stay inside, out of the sunlight for much of the day, basking in the air conditioning.

  2. Nothing said in this article about the effects of aging on the body’s ability to produce Vit. D as shown in the diagram.

  3. If you dont take advantage of the sunlight (less needed at high elevations) and get it from a pill, choose D3. It is one of the few vitamins that have actually shown value from a pill (also B12, but not E or C). For more info see

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