The newest superstar supplement (and I must say, I’m on board with the bandwagon) is vitamin D, which isn’t a vitamin at all as it can be synthesized by the body (when the skin is exposed to sunlight) – it’s actually a prohormone. Nonetheless, vitamin D is important to many bodily functions and research is finding that many Americans are deficient in it, which may be contributing to chronic diseases.
- Helps calcium absorption from the gut and maintains normal blood levels of calcium and phosphorus. If not enough calcium is absorbed from the intestines, the body will take calcium from the bones to normalize blood levels – which we obviously don’t want!
- Without adequate vitamin D and calcium, only 10-15% of dietary calcium and 60% dietary phosphorus is absorbed
- Prevents rickets (soft bones) in children, osteomalacia (weak bones) and osteoporosis in adults [see above mechanism]
- Recent research indicates that adequate stores of vitamin D may play a role in preventing many chronic diseases and conditions including cancer, hypertension, diabetes, allergies in children, multiple sclerosis
- One study reported that postmenopausal women who increased their vitamin D intake by 1100 IU of vitamin D3 reduced their relative risk of cancer by 60 to 77%
- Several studies have linked vitamin D deficiency and colon, prostate, breast ovary and esophageal cancer, with blood levels >20ng/mL reducing the risk by as much as 30-50% according to one study
- Likely plays a role in optimizing immune function
- May help prevent cardiovascular disease by inhibiting inflammation [chronic inflammation is a risk factor for heart disease]
Those that may be at risk of deficiency: elderly, obese individuals, dark skinned individuals, lack of exposure to sunlight, exclusively breast fed infants, diets that avoid dairy/egg products, those with limited sun exposure, after gastric bypass surgery, hospitalized patients.
Specific disease states that increase the risk of vitamin D deficiency include cystic fibrosis, inflammatory bowel disease, celiac disease, diabetes, pancreatic disease, kidney disease, cardiovascular disease, and liver disease
The test: Ask your doc to check 25hydroxyvitamin-D – there are a few different lab values they can check, but this is best indicator of vitamin D status in the body as it reflects the amount of vitamin D produced by the body and consumed (not in body tissues however).
How much do you need?
The Institute of Medicine recently came out with new [controversial] recommendations for vitamin D and calcium:
- 0-12 months — 400 International Units (IU)
- 1-70 years — 600 IU
- >70 years — 800 IU
Many other health professionals (MD’s and RD’s) agree that this isn’t enough to do all the amazing things listed above. I get that the IOM is playing it safe, but with 30-50% of the general population being deficient, and the tolerable upper limit (maximum amount considered safe) being 4000 IU/day, supplementing 1000-2000 IU per day is my general recommendation for teenagers on. If you’re deficient [which I encourage all my patients to get checked] you actually would need 50,000 IU
per month per week for about eight weeks and then a maintenence dose of 50,000 IU per month thereafter.
Sources of Vitamin D
Your body makes vitamin D when the skin is exposed to sunlight. However, it can be difficult to obtain the necessary amounts based on many variables affecting the amount synthesized including: season, length of exposure, sunscreen, skin color (melanin content – the more this pigment you have, the darker your skin is and more difficult to synthesize vitamin D), and time of day. Some researchers suggest that 5-30 minutes of sun exposure without sunscreen from 10:00 AM and 3:00 PM at least twice per week to the face, legs, arms or back should be adequate. However, you won’t find many health professionals recommending 60+ minutes of sunscreenless exposure per week due to risks for melanoma (skin cancer).
The best natural food source of vitamin D3 is fatty fish and some mushrooms contain D2. Fortified milk contains about 100 IU per 1 cup – meaning to meet the IOM’s recommendations, you would need to drink 6 cups per day (even of skim milk, that’s an extra 480 calories per day, or almost +1 pound per week – we won’t even talk about if it’s not skim milk); to meet my recommendations, 10-20 eight ounce glasses of milk per day!
Per the National Institute of Health, here’s what your blood test results mean:
<11 ng/mL (Deficiency) — Rickets in infants and children
<15 ng/mL (Insufficient) — Inadequate for bone and overall health
>30 ng/mL (Sufficient) — Proposed as desirable level and disease prevention
>200 ng/mL (Intoxication) — Considered potentially toxic
Many experts recommend blood levels closer to 50-75ng/mL for optimal health.
D2 or D3?
Vitamin D2 (ergocalciferol) comes from yeast, while Vitamin D3 (cholecalciferol) is found naturally in cod liver oil and oily fish such as salmon and can be obtained from sheep’s wool. Studies have had varied results, but many tend to think D3 is more effective at raising blood levels of vitamin D. However, if you are a vegan/vegetarian, D2 may be a better option and will still have positive effects.
Note: Make sure to take your vitamin D supplements with a meal containing fat – it is a fat soluble vitamin meaning that it needs fat to be absorbed.
Michael F. Holick, M.D., Ph.D. Vitamin D Deficiency. New England Journal of Medicine. 2007
Michael F. Holick, Rachael M. Biancuzzo, Tai C. Chen, Ellen K. Klein, Azzie Young, Douglass Bibuld, Richard Reitz, Wael Salameh, Allen Ameri, and Andrew D. Tannenbaum Vitamin D2 Is as Effective as Vitamin D3 in Maintaining Circulating Concentrations of 25-Hydroxyvitamin D J. Clin. Endocrinol. Metab. 2008 93:677-681 originally published online Dec 18, 2007
Maryann King, MPH, RD, CNSD, LDN The Expanding Role of Vitamin D The Support Line 2/2011 Dietitians in Nutrition Support Dietetic Practice Group p. 16-23