According to the Department of Health and Social Care
“Around 1 in 6 adults in the UK have low levels of vitamin D, which can lead to rickets, bone pain and disabilities”.
But that is not the whole story!
Apparently, vitamin D has an important role for our immune system and even in the prevention and reduction of cancer mortality. Indeed, according to a recent study which reviewed 27 academic medical articles on the association between vitamin D deficiency and COVID-19, severe COVID-19 patients presented more vitamin D deficiency compared with mild cases. Also, in another study conducted in 2019, which analysed data gathered on 6537 patients vitamin D supplementation was shown to significantly reduce total cancer mortality.
Given the importance of vitamin D, it is not surprising that The International Osteoporosis Foundation has developed and launched an interactive map that details global vitamin D deficiency levels. The aim is to make health professionals and governments aware of the deficiency of vitamin D in their own countries and urge them to take appropriate actions to correct it. Accordingly, “this will help improve and even saves lives” claims Judy Stenmark, CEO of the International Osteoporosis Foundation.
Now if you look at the map, you will see that The Swedish come out on top when it comes to vitamin D levels. Despite having very disparate levels of sunshine throughout the year it seems they perform better than most other countries in Europe. Even better than those Mediterranean sunny countries like Spain, Italy or Greece. But, how is that possible?
Well, it looks like the secret is their diet! Indeed, vitamin D is found in oily fish, such as salmon, sardines and mackerel which represent a major part of the typical Swedish diet. Even canned tuna seems to provide a good amount of vitamin D (See table below). So, it is possible to get enough vitamin D just from food? Even in those countries with low levels of sunlight? And what about those people who follow a vegetarian or vegan diet? Can they take a sufficient amount of Vitamin D just from food?
According to the National Institutes of Health Office of Dietary Supplements, we generally need between 600 and 800 IU of vitamin D daily. Now, although the body produces vitamin D when a person’s skin is exposed to direct sunlight not everyone can spend hours outside. Moreover, there is no definitive rule of thumb for how long someone should be exposed to direct sunlight to get a decent amount of vitamin D. Indeed, many factors affect how much vitamin D a person gets from the sun, such as time of the day, season, skin tone, amount of skin exposed, geographical area, etc. Hence, the alternative is food.
If you follow a vegan diet, it is possible to find vitamin D, especially in mushrooms. However, not all varieties “are fit” for the purpose. If you look at the table below that we developed according to data provided by the U.S. Department of Agriculture (USDA) some varieties are better suited for the task. We categorised some of the most common varieties so that you can shop smarter and select the most vitamin D-rich mushroom at the grocery store.
*We refer to the raw mushrooms not exposed to UV light.
Accordingly, Maitake mushrooms should be preferred when looking for a high level of vitamin D. Yet, considering that we need between 600 and 800 IU of vitamin D, assuming non-exposure to sunlight, we should eat more than 1Kg Maitake mushroom. However, we do not want to have indigestion! Do we? So?
Well, the good news is that mushrooms (similar to humans) have the ability to increase vitamin D amounts due to artificial UV-light or sunlight exposure thanks to a substance called “ergosterol” that converts into vitamin D when exposed to light.
Unfortunately, most commercially grown mushrooms are grown in the dark and, thereby, lack vitamin D. Yet, many food retailers have launched mushrooms which are grown in extra light to naturally enhance their vitamin D levels. This is why in some supermarkets you will find mushrooms varieties which were supposed to have 0 IU of naturally occurring vitamin D with a label claiming, “rich in vitamin D”. It’s important to review the Nutrition Facts Panel on your mushrooms’ packaging to check for vitamin D amount per serving.
Yet, understanding nutrition labels on food packaging could be tricky. Indeed, sometimes the amount of vitamin D is expressed as International Units (IU) and sometimes as micrograms (μg). Well, let’s clear up any doubts. 1 microgram of vitamin D is equal to 40 IU. So, following the National Institutes of Health Office of Dietary Supplements recommendations, we should get a minimum of 600 International Units (IU) which is equal to 15 micrograms (μg). You should check your mushrooms labels to see if you get closer to that threshold.
Also, you should prefer sun-dried mushrooms as they have significantly higher levels of vitamin D than raw mushrooms simply exposed to sunlight. Most interesting, dried mushrooms preserve significant amounts of vitamin D. This means that you can capture vitamin D in mushrooms and have a ready source of vitamin D through the fall, winter, and spring. And the good news is that you can do it yourself. Indeed, Paul Stamets, mycologist and medical researcher, in an article published in the HuffPost claims that the process is very simple and consists of a few steps:
1. Get fresh (possibly organic) mushrooms.
2. On a sunny day, slice the mushrooms and put them on a tray exposed directly to the sun for six hours from 10 a.m. to 4 p.m.
3. Before nightfall, cover the mushrooms with a layer of cardboard to block moisture from dewfall.
4. Repeat exposure to the sun from 10 a.m. to 4 p.m. the following day or any other dry sunny day.
5. Remove the mushrooms and finish drying thoroughly.
6. Store them in a glass jar or sealed container. Adding a tablespoon of uncooked rice as a moisture absorber will help keep the mushrooms dry. The mushrooms should be good for a year or more, depending upon the conditions.
7. Take 10 grams daily per person, about a small handful. Rehydrate in water for one hour. The mushrooms will swell. Then cook as desired.
Of course, no one insists that the consumption of mushrooms will have any kind of dramatic effect on your life; if you spend some time outdoors and you absorb enough sunlight you will probably be perfectly fine. Also, if you do not like mushrooms you can still get your recommended daily intake of vitamin D from fortified food or supplements. Still, is good to know!