After years of being heralded as a beneficial supplement, with many doctors testing blood levels and prescribing supplements to raise them, vitamin D is starting to become a bit controversial. Some doctors are questioning the wisdom of both testing and supplementation.
No one disagrees with the fact that vitamin D is essential. Until it began to be added to milk in the 1930s, weak bones (rickets in children and osteomalacia in adults) were major problems. Without enough vitamin D, the body can’t absorb calcium properly, and bones become thin, brittle, and sometimes deformed. In recent decades, studies have found that adequate levels of vitamin D also contribute to many other aspects of health, including:
- Heart health
- Muscle function
- Reduced cancer risk
- Healthier babies
- Less diabetes
- Less osteoporosis
- Stable mood
- Less inflammation
Conflicting Study Results
Despite a clear correlation between adequate vitamin D levels and less risk for many major chronic diseases, results of supplement studies haven’t been completely consistent. Some studies have found that elderly people who take vitamin D suffer from fewer fractures, but others have found no such benefit. Some, but not all, studies show that vitamin D supplements improve levels of blood sugar and reduce winter blues and respiratory infections.
Several factors could help explain these inconsistent results. Studies of vitamin D supplements have not routinely tested participants’ blood levels before starting supplementation. Yet, people whose vitamin D levels were high before taking supplements would not be expected to benefit in the same way as those who were deficient at the start. Different forms of vitamin D found in over-the-counter supplements and prescriptions from doctors don’t all have the same effect, but studies don’t always identify which form of vitamin D is being tested.
One research review examined how various vitamin D supplements affected mortality. It included 56 trials, with more than 95,000 people between the ages of 18 and 107. Elderly people who took vitamin D (but not those who took vitamin D) lived longer. People who took prescription forms of the vitamin (alfacalcidol or calcitriol) did not live longer and ran the risk of hypercalcemia, blood levels of calcium so high that they can be life-threatening.
Some experts theorize that vitamin D supplementation might increase harmful calcium deposits in arteries, because this effect has been seen in animal studies. However, human studies have found the opposite: vitamin D reduces calcification of arteries.
Form & Function
There are two forms of vitamin D in supplements: D (cholecalciferol) and D ergocalciferol). Most supplements in health food stores contain D. This is the form made by the human body after sun exposure, and it is absorbed and used more effectively than D. However, supplements prescribed by doctors often contain vitamin D—made with a process that has been patented by pharmaceutical companies.
Vitamin D doesn’t work in isolation in the human body and is most effective with some synergistic nutrients:
- Vitamin K: It inhibits calcification of arteries. Vitamin D is often taken with calcium and enhances absorption of the mineral. When taken in high doses, calcium can be deposited in arteries. Taking vitamin K with vitamin D helps to get calcium into bones, rather than arteries.
- Magnesium: Without adequate magnesium, vitamin D is less effective because it’s stored, rather than being used. The American Osteopathic Society estimates that about half of Americans are deficient in magnesium.
Vitamin D Tests: What They Mean
Not all experts agree on the optimum level of vitamin D in blood. Between 12 and 20 ng/ml (nanograms per milliliter) is considered sufficient to prevent a deficiency that could cause rickets. However, the Endocrine Society concluded that levels above 30 ng/ml are desirable for optimum function, and by this standard, nearly 8 in 10 American adults lack sufficient vitamin D.Blood levels above 50–60 ng/ml may produce adverse effects.
How to Get Enough Vitamin D
It’s best to get a vitamin D test and take supplements based on results. The Endocrine Society estimates that adults need 1,500–2,000 IU of vitamin D daily, in supplements, to achieve and maintain desirable blood levels above 30 ng/ml. Doses recommended by the federal government are lower:
- Ages 0–12 months: 400 IU daily
- Ages 1–70: 600 IU daily
- After age 70: 800 IU daily
To benefit fully from vitamin D, take a vitamin D supplement that also contains vitamin K. In addition, take at least 200 mg of magnesium daily. Vitamin D has traditionally been derived from animal sources, but there are vegan forms made from lichen. Because it is fat-soluble, vitamin D is best taken with fatty food.
Vitamin D is one of four fat-soluble vitamins (A, E, and K are the others). Take with some fat for better absorption.
Body Fat and Vitamin D: Men and women with belly fat, and women with overall excess body fat, have lower blood levels of vitamin D, likely because the vitamin is stored in fat instead of being utilized. In these situations, higher doses of vitamin D are needed for healthy blood levels.
Vitamin D and Kidney Stones: A recent study of healthy people found that taking 1,200 mg daily of calcium with 600 IU of vitamin D slightly increased risk for kidney stones. Taking that amount of calcium with 10,000 IU daily of vitamin D more than tripled the risk. However, other research has found that taking up to 1,000 IU of vitamin D daily did not increase such risk. Magnesium and vitamin K may help to prevent kidney stones.