Vitamin D or cholecalciferol is one of the 4 fat soluble vitamins. Because it is a fat soluble vitamin, toxicity is possoble and harmful when overdose. Besides vitamin K, vitamin D is a vitamin that can be synthesized by the human body.
First, let’s talk about the forms of vitamin D once it’s ingested.
Form #1: When vitamin D is processed in the liver, it turns into a form called calcidiol. When your doctors look at the blood test result to rule out vitamin D deficiency, they look for calcidiol.
Form #2: When vitamin D is sent to the kidneys to be processed instead of the liver, it turns into calcitriol. Just because the doctor does not look at calcitriol as the very first indicator, calcitriol is still an important indicator because long term deficiency of vitamin D will cause a low level of calcitriol.
Interestingly, calcidiol can be converted to calcitriol if needed. Usually, people on dialysis have low blood calcium, which is treated with calcitriol. So, it’s not too bad an idea for such population to get enough vitamin D through foods or sunshine because vitamin D in calcidiol form can be converted to calcitriol.
1/ Functions of vitamin D
- First, vitamin D helps increase calcium absorption in the stomach.
- Second, vitamin D keeps a healthy balance of phosphorus and calcium in the blood through which it ensures good bone metabolism.
- Just a note: bone health is determined not by only calcium but also by vitamin D intake, phosphorus intake, sodium intake, and resistance training.
- Third, with its important role in bone metabolism, vitamin D is vital for healthy growth among children and prevent osteoporosis in adults.
- Lastly, vitamin D may lower the risks of certain cancers: skin cancer, prostate cancer, breast cancer, and colon cancer.
2/ What happens if you have vitamin D deficiency?
I don’t know about vitamin D deficiency prevalence in other countries, but according to the Center of Disease Control, in the in U.S, among healthy weight children, 21% of them was diagnosed with vitamin D deficiency. Among U.S overweight children, about 29% of them have vitamin D deficiency. For the obese U.S children, there are 35% of them have vitamin D deficiency. And for the morbidly obese kids, about 49% of them develop vitamin D deficiency. What? The heavier the kids, the higher risk of vitamin D deficiency? True. That’s possibly because the weight may indicate life style and eating habits: more sedentary (less playing outside in the sun) and less healthy eating habit (gulf down on ice cream, milk shake, and frappuccinos instead of plain cow’s milk).
And it’s not just among U.S children. The National Health and Nutrition Examination survey showed a prevalence of 42% U.S adults had vitamin D deficiency with the highest rate among Hispanics (69% of them) and African Americans (82% of them). How so? Not really genetic issues here. It’s more about lack of knowledge and low economic status.
Sorry going off track, let’s go back to what happens if we don’t have enough vitamin D
First, long term vitamin D deficiency may directly cause osteoporosis. How? Ok we’re told calcium is essential for bone growth. And, bone grows all the time, not just when we’re little children. It is called bone “remodeling”. Bones have bone cells and when the cells die, they need to build new ones. And, calcium is needed for that. We know vitamin D increases calcium absorption in the stomach. So, when there is lack of vitamin D, calcium absorption is decreased.
Second, the one disease associated with vitamin D deficiency and calcium deficiency: rickets. Rickets is caused by osteomalacia (literally bone softening) and treatable with high vitamin D doses, such as cod liver oil. That disease is essentially due to the softened bones, especially the long bones in the legs, causing the legs to bow out. While it is most prevalent among young children, it can happen in adults, too, if the case is severe enough. See pictures
Third, there is a link between low vitamin D level and high blood pressure.
Fourth, low vitamin D level causes muscle weakness.
Fifth, vitamin D deficiency may cause kidney diseases by causing low phosphate levels. In other words, phosphates are lost in urine. Vitamin D2 (in plants aka mushrooms or supplement with ergocalciferol as active ingredient) can treat this condition.
Sixth, low vitamin D level may cause overactive parathyroid glands directly related to…low level of vitamin D in blood.
3/ How much vitamin D do you need? I’m gonna list as International Units (IU)
- 0-12 months: 400 IU/day
- 1-70 years: 600 IU/day
- Over 70 years: 800 IU.
4/ Who’s at risk of vitamin D deficiency
The Center of Disease Control recognizes the following groups as population with high risks of vitamin D deficiency:
Infants who consume only breast milk: Yes, breast milk is nutritious and important. However, it cannot be relied as the only source of vitamin D. Look, cow’s milk has been venerated as the good source of vitamin D actually does not have this vitamin D naturally. It’s the human who put vitamin D into that bottle in the form of vitamin D2 or ergocalciferol. Similarly, breast milk does not contain much of vitamin D: there is only 78 IU of vitamin D per liter of breast milk IF THE MOM IS IN OPTIMAL HEALTH EATING OPTIMAL DIET RICH IN VITAMIN D. And how much infants need? They need 400 IU of vitamin D per day. Now, if the mother does not eat healthy diet or lacks vitamin, then her vitamin D in milk drops from 78 IU to …25 IU per liter. I don’t think infants drink more than 4 liters of breast milk a day to meet their vitamin D requirement.
People above 50 years old: Aging process causes poorer digestive functions and liver functions (liver is what makes vitamin D through sun exposure). On top of that, older people tend to not enjoy being outdoor due to hot or cold temperature. The consequence is even worse among women because by 50 years of age, most of them enter menopause-lower hormones mean higher risks of bone fractures.
People with dark skin pigment: African Americans have higher risk of vitamin D deficiency because the skin needs to be exposed to the sun much longer to be able to make vitamin D. How much longer? Depending on the pigmentation.
People who lack sun exposure: People may avoid skin exposure for many reasons: religion (Muslim women who cover top to toe), fear of getting skin cancer (you hardly get any skin cancer if you exposure to the sun for 1-2 hours just 2-3 times a week), and using too much sun block, and vanity (mostly among Asians who want whitening products instead of tanning lotion).
People with poor digestive functions: people who just have bariatric surgery, people who can’t produce certain bile and enzymes.
People with Anorexia: fear of gaining weight may cause unhealthy eating habits such as avoiding foods with natural fats (nuts, oil, dairy) or avoiding adding fat in cooking process). Remember, you need fat to absorb vitamin D; otherwise, you’re just wasting vitamin D into urine.
Vegans with improper diet and lifestyle: these people are at high risk of vitamin D because they avoid dairy and eggs while avoiding supplement and sun exposure altogether.
Overweight and obese people: these people usually exhibit unhealthy and imbalance diets, which may contribute to a diet lack in vitamin D. However, these people are at risk mostly because they need higher level of vitamin D. Vitamin D is estimated based on individual body weight. Thus, heavier people need greater amount of vitamin D. When you combine this unhealthy eating habit and lifestyle, you can see why a great percentage of overweight and obese people suffer vitamin D deficiency. Since obesity becomes pandemic disease; you bet vitamin D deficiency has been considered as pandemic issue since 2008.
5/ How do we get vitamin D from the sun?
Good news to us all: vitamin D synthesized by our own body does not cause toxicity (which may cause calcification of arteries).
Actually it is the UVB that is used to make vitamin D. The ability of our body converts UVB to vitamin D (provided that the liver is healthy) depends also on the color of the skin. For African Americans, the body may need 1 hour to several hours sitting in the sun. For Asians, the pigmentation of the skin also requires longer time to make enough vitamin D: about 30 minutes to over one hour. For Caucasians, they usually need just 15 minutes in the sun.
However, the rule of thumb is to stay in the sun until you can see your skin turns SLIGHTLY PINK or changing color (if your skin is darker and hard to see the pinkness).
Also, it may be worth noting that a product with SPF greater than 8 can block UVB so much that it prevents vitamin D synthesis. The best strategy is to leave some part of your body exposed to the sun (feet, hands, lower legs, or the back) while you have a chance go out in the sun for a hour or so
Some people think they can get vitamin D by sitting next to a glass window. Well, it appears that UVB can’t penetrate glasses, so siting indoor next to a window does not help.
6/ How do we get vitamin D from food?
Fishes are great sources for vitamin D. However, make sure you select fishes that are low mercury and do not consume more than 12 oz a week (336 g/week). For pregnant women or women who plan on getting pregnant, please make sure you do not consume more than 6 oz per week (180 g). Whether you’re pregnant, female or male, avoid these 4 fishes: shark, swordfish, king mackerel, and tilefish.
For milk drinkers, please keep in mind that vitamin D is fat soluble. You need fat to get the benefit of vitamin D (and also vitamin A). Therefore, those who drink away fat free and low fat (1%) milk don’t get the benefit of these vitamins-hello, you just drink the calories without these micro nutrients. I repeat, do not avoid fat while you want to get vitamin D.
Salmon, 85 g (3 oz), 112% vitamin D
Tuna, 85 g, 39% vitamin D
Egg, 1 large, (vitamin D comes from the yolk so eat your egg yolk): 10% vitamin D
Cod liver oil, 1 teaspoon or 5 mL: 110% vitamin D.
Milk, 250 mL (1 cup), 32% vitamin D
Sardines, 3.5 oz, canned, 44% vitamin D
Mushrooms, 100 g (3.5 oz), 6% vitamin D
7/ What about getting vitamin D from supplement:
I don’t like supplements at high doses on a daily basis. Some people with medical condition can take high doses, but that must be done under medical doctors’ supervision.
Okay, vitamin D supplements come in 2 forms.
It is either vitamin D2 or vitamin D3. Vitamin D2 is ergocalciferol. Vitamin D2 is the form of calcium you find in mushrooms. This is the ingredients that we put in foods (e.g. milk). Vitamin D3 is cholecalciferol, which is abundant in animal based, such as egg yolk.
So vitamin D2 vs vitamin D3: they say that at low dose, both are equally effective. However, at higher doses, vitamin B3 appears to be more effective than vitamin D2. Research papers also indicate that people who use vitamin D2 supplement have significantly greater risks (of overdosing) than those who use vitamin D3.
Interestingly, doctors usually prescribe vitamin D2 to patients. Why? I don’t know. And I don’t want to guess, either.
Verdict: stick to vitamin D3.
Toxicity is possible. When you consume so much of vitamin D through foods and supplement pills, you may risk yourself other conditions:
- Rapid pulse
- Loss of appetite
- Calcification of arteries (causing blockage): this is the real serious medical condition that can cause death.
Therefore, it’s important to know that you must not exceed the upper level of vitamin D. Many vitamin D supplements out there are way above the following values. Why? Well, in the U.S, supplements are not regulated by FDA. So the manufacturers can put whatever they want into your pills and brag about health benefits without warning you something like you can overdose and harm yourself by taking vitamin supplements at high dose as what they’re trying to sell to you.
Upper level is set as followed:
- 0-6 months: 1000 IU/day
- 7-12 moths: 1500 IU/day
- 1-3 years: 2500 IU/Day
- 4-8 years: 3000 IU/day
- 9 years and older: 4000 IU/day