Highlights:
- Vitamin D the sunshine vitamin is important for calcium and phosphate uptake from food. It is also needed for bone growth and bone remodeling
- Our bodies can make vitamin D from skin exposure to sunlight, but we often do not get enough sun exposure
- National Academies recommends supplementation of 600 IU for adults 19-70 years and 800 for adults over 70, with a maximum supplementation of 4000 IU per day
No supplement stack will be complete without at least a discussion of vitamin D. This might be one of the most studied and talked about vitamin in recent years, and for a good reason. Here is some of what is currently known about Vitamin D supplementation.
The biology:
Vitamin D is essential for calcium and phosphate uptake from food. It is also needed for bone growth and bone remodeling. Together with calcium, vitamin D is essential for protecting adults from osteoporosis. Vitamin D also helps reduce inflammation and regulates cell growth, immunity and glucose metabolism. Suffice it to say, it is pretty important to maintain a healthy level of vitamin D without exceeding a safe limit.
Traditionally most people get their vitamin D from sun exposure where the precursor 7-dehydrocholesterol is converted into the active form of vitamin D called calcitriol. Vitamin D taken in from food can be D2 or D3 and both are converted into the active form by the body (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/).
Vitamin D from plant-based food sources are taken as vitamin D2 or ergocalciferol. Many foods are fortified with vitamin D2 (e.g milk, yogurt, plant-based milks, cereal etc.). Another rich source of vitamin D2 is sun-exposed mushrooms. The best dietary source of vitamin D3 or cholecalciferol is fish and to a lesser extent, eggs. Both vitamins D2 or D3 can be taken in as oral supplements. It is generally better to take vitamin D with some fat for optimal intestinal absorption.
Since we make Vitamin D from sunlight exposure and can take in vitamin D from food sources, it is a good idea to have some ideas as to how much Vitamin D you are producing and how much to take in from food. Generally in the western world, unless we are exposed to a lot of sunlight, we may not be producing sufficient Vitamin D. The situation gets even worse, if we are wearing sunscreen. SPF30 sunscreen will inhibit >95% of Vitamin D production.
Clinical benefit:
The role of Vitamin D in many essential biological processes is well established. However, it is always a good idea to look at what the clinical data says about benefits of Vitamin D supplementation. So it is important to note that despite all the hope, a recent large prospective clinical trial studied whether daily 2000 IU of Vitamin D supplementation had any beneficial effect on the prevention of cardiovascular disease and cancer and did not find any benefit (https://www.nejm.org/doi/full/10.1056/NEJMoa1809944). A 2014 Cochrane review of 31 trials of vitamin D with or without calcium found that Vitamin D taken together with calcium, but not vitamin D alone, lowers bone fractures (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7032685/). So naturally this raises the question as to whether vitamin D supplementation is needed and whether it should be only taken together with a calcium supplement.
General guidelines on vitamin D:
How much Vitamin D supplementation is recommended?
Based on recommendation from the National Academies of Sciences (https://ods.od.nih.gov/factsheets/vitamind-healthprofessional/):
Recommended daily allowance (both men and women):
- Ages 19 – 70 years: 600 IU per day
- Ages 70+ years: 800 IU per day
Tolerable upper intake levels (UL) (both men and women):
- Ages 19+ years: 4000 IU per day
How much sun exposure is sufficient to get all of our vitamin D from sunlight exposure alone? Vitamin D researchers suggest a wide range, 5-30 minutes of sun exposure daily or at least 2 days a week without sunscreen with exposed face, arm, hands and legs. Skins of the elderly or those with darker skin do not produce as much vitamin D. Since UVB does not penetrate glass, sun exposure through a window does not produce vitamin D.
What is a healthy level of vitamin D in serum?
- >/= 20 ng/ml but < 50 ng/ml*
*Tests measure a Vitamin D precursor molecule called 25(OH)D.
Safety:
There are important safety considerations with vitamin D supplementation. There are clear risks associated exceeding the tolerable upper intake level (UL) mentioned earlier. It should be noted that supplementation less than the UL can also lead to adverse health effects over time. Excess amounts of vitamin D can lead to hypercalcemia (excessive calcium), which in turn can lead to effects such as nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones. There are also contraindications if you take certain medications including calcipotriene, digoxin, diltiazem, atorvastatin, thiazide diuretics. Also taking a vitamin D supplement within two hours of taking an aluminum-containing antacid can increase the level of aluminum the body absorbs. Here is a more complete listing of (https://www.webmd.com/vitamins/ai/ingredientmono-929/vitamin-d).
What I take:
I have been taking 4000 IU of vitamin D3 about 4 days a week. But after a closer review of the data, I am seriously considering whether I should reduce my supplementation. I also plan to have my serum 25(OH)D level tested. Here is a real example of how evidence should and does change our minds. We are continually trying to optimize both the list of supplements as well as their doses.