How to Find Tested and True Vitamin D at the Best Value

Supplement image courtesy of worradmu/

Vitamin D is a fat-soluble vitamin that is the third most popular supplement in America today and one of Consumer Reports “11 supplements to consider.”* There are two major forms of vitamin D; D2 (ergocalciferol) and D3 (cholecalciferol).  Both vitamin D2 and D3 appear to be absorbed with equal efficiency and, at moderate doses, are equally able to raise the biologically active form of vitamin D – the clinical measure of vitamin D status.


Vitamin D2 (ergocalciferol) is made by the conversion of a sterol found in plants and yeast and is used in some dietary supplements.

Vitamin D3 is produced naturally in human skin exposed to ultraviolet B light (UVB) and occurs in some animal products, such as cod liver oil, and, in smaller amounts, in other fatty fish such as herrings, mackerel, sardines, and tuna. Vitamin D3 is the most common form used in dietary supplements and is the form generally used to fortify foods such as milk (which naturally contains a small amount of vitamin D3).

Many people are deficient in vitamin D, which partly explains the growth in its supplementation use, especially those who are over 60, live at northern latitudes, have darker skin, or rarely spend time outside.  Research supports common sense in that residents of the northern U.S. and Canada report significantly lower Vitamin D blood levels in the winter.  Recent studies show that many young people also have low blood levels of vitamin D and that reduced vitamin D levels may be associated with being overweight.

Vitamin D: Claims and Purported Use

The body of research on vitamin D emphasizes its partnership with calcium and phosphorus. By regulating their levels of absorption in the body, vitamin D enhances bone strength.  Taken with calcium, vitamin D can help decrease post-menopausal bone loss and prevent osteoporosis (loss of bone density), as well as, improve tooth retention in the elderly. In girls ages 9 to 13, regular supplementation with calcium and vitamin D has been shown to significantly increase bone density and bone strength (measured in arms and legs) compared to a placebo. Additionally, vitamin D treats and prevents rickets in children and osteomalacia (bone softening) in adults. Given to breast-fed infants, vitamin D may help increase bone density.

Newer studies have evaluated vitamin D’s potential to reduce the risk of everything from some common cancers and multiple sclerosis to diabetes, hypertension (high blood pressure), and age-related muscle weakness.  A relatively new meta-analysis (combined results of several studies) revealed that people taking vitamin D supplements had a 7% reduction in total mortality rates (number of deaths in a population).  With concerns of sun exposure’s link to skin cancer, more people are seeking supplements to improve their vitamin D levels.  The following vitamin D products listed below passed independent testing and offer the best value.

Pick Your Preference


Source Naturals Vitamin D-3 liquid drops – ideal for folks who want to easily adjust the desired amount at the lowest price.

Twin Lab D-3 Dots  – small dissolvable tablets

Simply Right Vitamin D-3 – softgel


Carlson Super Daily D-3 for Kids  – the liquid form makes it easy for the parents to adjust the amount provided.

Selected Potential Side Effects

Extremely large amounts might cause weakness, fatigue, headache, and nausea, though side effects are rare.

Selected Drug Interactions

Might reduce the effectiveness of some medications, such as atorvastatin (Lipitor), other heart medications, birth control pills, HIV/AIDS drugs.

Suggested Dosage

Vitamin D is measured as micrograms of cholecalciferol or in International Units (IUs) of vitamin D activity.  One microgram equals 40 IU.  The RDAs for vitamin D intake are based on amounts required for bone health.

Infants up to 1 year AI is 400 IU (only if infant is not getting sufficient sunlight exposure)

Ages 1-70 years RDA is 600 IU

Ages 71+ RDA is 800 IU

Infants up to 6 monthsUL is 1,000 IU

Infants 6 to 12 monthsUL is 1,500 IU

Ages 1-3 years UL is 2,500 IU

Ages 4-8 years UL is 3,000 IU

Ages 9+ UL is 4,000

Reference Guide for Tested and True Dietary Supplements

Tested and True: Fish Oil

Tested and True: Krill Oil

Tested and True: Multivitamins

Tested and True: Vitamin D

Tested and True: Coenzyme Q10 (CoQ-10)

Tested and True: Glucosamine and Chondroitin

Tested and True: Probiotics

Tested and True: Muscle Enhancers – Creatine

Tested and True: Muscle Enhancers – Branched Chain Amino Acids (BCAAs)

Tested and True: Nutrition Bars

Tested and True: Nutrition Drinks & Powders

Tested and True: Weight Loss Accelerators and Appetite Controllers

Tested and True: Mood Booster SAM-e

Tested and True: Mood Booster St. Johns’ Wort

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*reference: Consumer Reports Health

About Dave Barnas, M.S., CES, NASM-CPT

Dave is the true health guy. He is the founder and owner of True Health Unlimited, LLC, a personal health and fitness company in Tolland, CT & Wellness Writers, a subscription wellness newsletter service that incorporates live & virtual wellness workshops for companies across New England. Dave earned both a Bachelor's (1998) and Master's Degree (2000) in Nutritional Science from the University of Connecticut, and also holds certifications as a National Strength and Conditioning Association Certified Personal Trainer, National Academy of Sports Medicine Certified Personal Trainer and Corrective Exercise Specialist, Aerobics and Fitness Association of America Group Instructor, and Nutrition Specialist. He's also the lead author for four published works. Dave has over 20 years of combined experience in nutrition counseling, dietary supplement advising, personal training, corrective exercise training, health coaching and public speaking. In addition, he's spent over 25 years studying spirituality, meditation, and personal growth strategies. Dave's clients are all ages: youth, college championship level athletes, folks in their retired years, and everywhere in between. He's worked with three of the nation's leading physicians as a dietary supplement advisor and been a guest lecturer at Harvard University, Yale University, UConn, St. Joseph College and various church groups, health clubs, and high schools. In 2013, he was invited to Whole Foods Market to share his Real Food Therapy Guide. And in 2015, Dave's funny "Snowga" (yoga in the snow) video caught the attention of The National Weather Channel, who aired it to shake off cabin fever and bring laughter. In 2016, Dave & Hollie (his wife) founded Wellness Writers and deliver evidence-based Wellness E-newsletters to spread a message of health and happiness to various businesses throughout the US. Dave currently serves as a personal trainer in Tolland as well as a wellness coach and writer for several businesses, gyms and wellness facilities throughout the US.

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