KNOWN AS THE “SUNSHINE PILL” for its supposed ability to mimic the effects of sunshine on health, vitamin D supplements are a billion-dollar industry.
People take vitamin D supplements for a variety of reasons, mental and physical. Some take it if they feel sad, perhaps as the result of the winter blues, for example. Others take it because vitamin D supposedly plays a role in bone health.
But before reaching for the pillbox, you need to know these seven facts about vitamin D supplements and how they work.
WHAT IS VITAMIN D AND HOW DOES IT AFFECT HEALTH?
Vitamin D appears to enable the body to absorb calcium and phosphate — both of which are important for bone health and for muscle function. The vitamin influences cell metabolism and growth, as well as overall immune system functioning. Vitamin D is also associated with a healthy gut microbiome.
The United States' Centers for Disease Control and Prevention recommends mothers who breastfeed their babies supplement their children with vitamin D, and that those who feed their babies infant formula also use formula that contains vitamin D. That is because too little vitamin D is associated with rickets, a condition that is characterized by soft or weak bones.
Beyond bone health, there is evidence that vitamin D plays a role in cancer, too. One study found vitamin D supplementation reduces cancer mortality by 25 percent. The idea is that vitamin D may influence tumor biology, making them less aggressive and less likely to proliferate.
Vitamin D deficiency can result from various problems, like inadequate Sun exposure, digestive problems, and kidney issues. Symptoms may include mood changes, bone loss, fatigue, and muscle, joint, and bone pain.
DOES VITAMIN D AFFECT MENTAL HEALTH?.
Different experts have different perspectives on this. As Inverse previously reported, Kathleen Holton, associate professor at American University and a nutritional neuroscientist, says low vitamin D can disrupt normal neurotransmission, and that in turn can lead to mental illness.
Others are more cautious about drawing conclusions. Margherita Cantorna, medical microbiologist and immunologist at Pennsylvania State University, tells Inverse that human brain cells have vitamin D receptors, suggesting that vitamin D is important. But there haven’t been sufficient studies in humans to determine what exactly this means for mental health, she says.
WHERE DOES VITAMIN D OCCUR NATURALLY?
Vitamin D is found in certain foods, including oily fish, mushrooms, eggs, and foods that have been artificially supplemented to contain vitamin D, like milk. The body also produces its own vitamin D when exposed to sunlight.
The way it works is that when sunlight touches our skin, we produce of vitamin D through the conversion of cholesterol in our skin cells, according to researchers at Yale University.
DO VITAMIN D SUPPLEMENTS WORK?
There is plenty of debate about vitamin D supplementation, and about the role of vitamin D in human health.
Vitamin D is most famous for promoting bone health, but a recent scientific review published in 2018 concluded that vitamin D supplementation did nothing to increase bone mineral density or to decrease bone fractures in people who already had normal vitamin D levels.
But according to the National Institutes of Health, vitamin D supplements are an effective way to raise blood vitamin D levels — if needed.
“Whether vitamin D supplements 'work' depends on whether you are deficient, low, or adequate in vitamin D,” Paul Thomas, a nutrition scientist who works with the National Institutes of Health Office of Dietary Supplements, tells Inverse.
“If you get enough vitamin D from food and Sun, vitamin D supplements should not be expected to provide any additional benefits.”
Thomas says that the recommended daily intake of Vitamin D from all sources is 15 mcg (600 IU) for people from 14-70 years old.
“Adequate [blood] levels range from 50-125 nmol/L or 20-50 ng/mL, depending on how the results are reported,” Thomas explains.
HOW CAN I RAISE MY VITAMIN D LEVELS?
People don’t tend to get enough vitamin D from food alone. Rather, the most important natural source of vitamin D comes from exposure to sunlight. But as people spend more time inside and use sunscreen to ward off skin cancer, vitamin D production catalyzed by the Sun decreases. According to a 2017 study, this may mean more people have vitamin D deficiency compared to earlier times in human history.
The shorter, colder days of winter can also reduce our time spent in the sunlight, and so decrease vitamin D production, leading some experts and doctors to recommend supplementation through the winter months.
The Cleveland Clinic says that 10-15 minutes of sunlight exposure to the face, legs, arms, or back a few times a week may provide sufficient vitamin D.
If you prefer to take a tablet every day, then vitamin D supplements are often affordable and generally considered safe, but recommended dosages vary widely depending on the brand. Whatever you think may be best, speak to your doctor before you take a pill.
HOW LONG DO SUPPLEMENTS TAKE TO KICK IN?
The good news is that it is easy to rapidly increase your levels of vitamin D to healthy levels.
“Your blood levels of vitamin D should rise within days of increasing your intake of this nutrient no matter from what source — supplements, foods, or [adequate] sun,” Thomas says.
WHAT EFFECTS SHOULD I NOTICE?
Here's the catch: Unless you have rickets or another extreme symptom of vitamin D deficiency, then you likely won't notice the difference at all.
If you are very deficient, Thomas says, then “any bone pain and muscle seizures and spasms should subside."
"For the vast majority of people, even those with low but not deficient levels, taking extra vitamin D will not provide any short-term noticeable benefits like feeling better, having more energy, or improvement in mental focus."
To get those kinds of benefits, you may be better looking beyond the pill box and to other health-boosting activities.
托马斯说，对于14-70岁的人，所有来源建议的每日维生素D摄入量建议为15 mcg（600 IU）。
“适当的[血液]水平范围为50-125 nmol / L或20-50 ng / mL，这取决于报告结果的方式，” Thomas解释说。