Almost everyone who comes to see me has questionable vitamin D levels, and I always advise them to have an inexpensive finger-stick vitamin D test. How can we tell if people are low or deficient in vitamin D? Living in the North of England (or anywhere in the United Kingdom) automatically puts a person in the high-risk category. The UK has a 6-month “vitamin D winter” because of the northern latitude. If you live above the 35th parallel -in Europe that’s north of Crete, and in the US that’s north of the Georgia-Tennessee border - there will be at least a month or two during winter when the sun’s UVB rays do not reach the earth. Since UVB is the type of light our skin uses to synthesise vitamin D, we either have to
1) eat foods that contain it (and there aren’t many),
2) supplement, or
3) rely on our body’s stores.
If you’re not a chemistry genius, then the ins and outs of Vitamin D synthesis might make your eyes cross. If you want to see the link explaining this process I’ll include it in the references.
Here are the cliff notes: vitamin D is a fat-soluble vitamin, which means we store it in our fat cells (and that’s one good reason not to be a rail-skinny supermodel). Then in the winter when UVB levels are nonexistent or when we’re not able to spend time in the sun, enzymes from the liver and kidneys release the vitamin D from our fat cells for use in other body systems. And what a job it has! Here are a few of the things that the body uses vitamin D for:
The gastrointestinal tract
Mood (depression, bipolar, manic depressive, etc).
Cancer prevention. Let me write that again -
Hormone balance - which means it’s part of:
blood sugar balance
And these are just ones I can think of off the top of my head. I confess, I did cheat a little bit in that list, because mood and immunity are all tied up in gastrointestinal health. I’ll list a couple of those studies in the reference section, just in case you’re not dribbling after going over that Vitamin D Metabolism paper.
Hopefully after reading the paragraphs above, you’ll agree with me that Vitamin D is extraordinarily important in most aspects of health. And the lack of it potentially sets people up for serious. health. problems. Even though too much vitamin D can cause problems as well, here in the UK, Public Health England issued a blanket statement in 2016 for everyone over the age of 1 year to supplement during the autumn and winter. This is a positive step forward, but would be more useful to individuals if there were annual tests to establish vitamin D status, as some people are more at-risk for deficiency than others. Nine-to-Five office or indoor workers are at greater risk, as are people with darker skin shades. Equally at risk are ladies who, for cultural reasons, don’t leave the house unless they are mostly covered. And some poor souls are genetically cursed and just don’t make the enzymes to metabolise vitamin D from fat storage, or store it properly. Then there is sugar.
Most people know that everything you eat turns to fuel, or “sugar.” Many people know that there are several types of sugar, the most plentiful being glucose. Table sugar (and most natural sweeteners like honey and maple syrup) are a fructose-glucose combination - you might know this as sucrose, which is 50% fructose and 50% glucose. The unfortunate relationship between fructose and vitamin D is that a high intake of fructose increases enzymes that break down vitamin D, while reducing the number of enzymes that synthesise vitamin D. Yikes. Now I’m not saying you should put down the donut and back away from the table, but be aware that self-rationing your sugar intake can do much more than simply prevent obesity and tooth decay.
Which brings me to: what foods should we eat to boost vitamin D levels? There aren’t very many - and they become less available the closer you are to the equator. Makes sense, since the closer you are to the equator, the more UVB you’ll have available year-round. But Vitamin-D supplying foods are salmon - a 4oz serving will give you 128% of the RDA for vitamin D. Sardines are also a good source, with a 3oz serving giving 44% RDA. Other notable foods are tuna steak (not canned tuna), eggs, and shiitake mushrooms are a small source.
If you don’t get many of the foods on that list, you may want to consider supplementation. The amount you supplement depends on your lifestyle factors (mentioned above) and your blood levels. It’s a good idea to get tested first, then seek the help of a nutritionist who can give you a good idea of the amount needed to supplement to correct any deficiencies and/or maintenance.
But by far the best way to get adequate vitamin D is just getting into the sunshine for about 15 minutes. The mechanism for vitamin D synthesis from sunshine is auto-regulated, so once you get enough, you can remain out in the sun (with adequate protection, such as sunscreen) but your body will efficiently shut down the production for that day.
To your health!
1. Vitamin D Metabolism, Mechanism of Actions, and Clinical Applications https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3968073/
2. Serotonin in the Gastrointestinal Tract https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2694720/
3. Overview of Gut Immunology https://link.springer.com/chapter/10.1007%2F978-0-387-09550-9_1
4. The new guidelines on vitamin D – what you need to know https://www.nhs.uk/news/food-and-diet/the-new-guidelines-on-vitamin-d-what-you-need-to-know/
5. 5 Nutrients You’re Deficient In… If You Eat Too Much Sugar https://www.thepaleomom.com/5-nutrients-youre-deficient-in-if-you-eat-too-much-sugar/?cn-reloaded=1
6. Chronic High Fructose Intake Reduces Serum 1,25 (OH)2D3 Levels in Calcium-Sufficient Rodents https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981704/
7. Excessive fructose intake causes 1,25-(OH)2D3-dependent inhibition of intestinal and renal calcium transport in growing rats https://www.physiology.org/doi/full/10.1152/ajpendo.00582.2012
8. Overview of Sunlight Exposure Messages https://www.nice.org.uk/guidance/ng34/evidence/expert-paper-7-overview-of-sunlight-exposure-messages-pdf-2311152883