Vitamin D — “the sunshine vitamin” that our bodies make when we’re exposed to sunlight — is critical to our health.
It’s essential for healthy bones and teeth, inflammation regulation, immune system support and other tasks.
A new report, presented at the American Heart Association’s Scientific Sessions 2023 conference, suggests the US recommended dietary allowance of vitamin D might be too low to reach the optimal levels for certain people, particularly those with heart problems.
So researchers at Intermountain Health, a western US health care network, are conducting an ongoing clinical trial to examine this topic.
Their study includes 632 participants who have experienced a heart attack or other type of cardiovascular problem. One group of participants received standard care, while the other received vitamin D supplements as needed to reach 40 nanograms of vitamin D per milliliter (ng/mL).
Their preliminary results showed that most people needed significant levels of vitamin D supplements to reach that level.
In fact, 51% of the participants needed 5,000 to 8,000 international units (IU) — 10 times higher (or more) than the current RDA of 600 IU for most people.
And 14.6% of participants needed 10,000 IU or more to reach optimal vitamin D levels.
Earlier studies found a link between low levels of vitamin D and an increased risk of heart attack or stroke. “However, the reasons behind this association are not clear,” Dr. Cheng-Han Chen, a cardiologist who was not involved in the study, told Medical News Today.
Some experts think “vitamin D receptors in cells throughout the vascular system are involved in blood vessel inflammation, which could in turn promote heart disease,” Chen added.
If their ongoing study “shows that achieving a vitamin D level of [more than] 40 ng/mL reduces the risk of adverse cardiovascular events, clinicians should be more proactive in testing and treating low vitamin D levels,” said study author Dr. Heidi May, a cardiovascular epidemiologist with Intermountain Health.
“Currently, we are following participants until there have been enough [cardiovascular] events that have occurred so we can compare if treating low vitamin D reduces cardiovascular outcomes compared to not actively treating low vitamin D,” May added.
What is vitamin D?
Vitamin D is an essential vitamin that your body makes when your skin is exposed to the ultraviolet rays in sunlight. It can also be found in some foods and in supplements.
Research has found that vitamin D plays an important role in the immune system, and it may reduce the risk of autoimmune diseases such as diabetes, asthma and rheumatoid arthritis.
It’s also critical for bone mineralization, the lifelong process by which minerals — particularly calcium and phosphorous — are added to your bone tissue to help it strengthen and grow.
The current recommendations for vitamin D intake are:
- Infants to 12 months: 400 IU
- Children and adults 1 to 70 years: 600 IU
- Adults over 70 years: 800 IU
- Pregnant or lactating women: 600 IU
Vitamin D from sunlight
Most vitamin D is made by your body when UV rays reach your skin; the vitamin is then stored in fat cells in your body.
People at risk of low levels of vitamin D — including people with disabilities, infants, the elderly and anyone who lives at far northern or southern latitudes during winter — also risk a loss of bone density and a subsequent increased chance of fractures.
People with darker skin have more melanin, so less UV light is absorbed to create vitamin D, according to UCLA Health. Therefore, they need more sun exposure to produce vitamin D than people with lighter skin.
One study revealed that during summer, with just 25% of the body exposed to the sun, about eight to 10 minutes of sunshine at noon produces the recommended amount of vitamin D.
But in winter, with 10% of the body exposed due to cooler temperatures, nearly two hours of sun exposure at noon is needed to produce enough vitamin D.
Vitamin D deficiency
Infancy and childhood, when bone growth is rapid, are important ages for getting enough vitamin D. Vitamin D deficiency in children can cause rickets, a softening of bone tissues that can lead to the deformed bones and joints, including bowlegged legs.
Some studies suggest a link between low vitamin D exposure and a higher risk of allergies in children. For example, children who live closer to the equator have lower rates of allergies and fewer prescriptions for epinephrine auto-injectors (EpiPens).
In most people, however, a short-term vitamin D deficiency doesn’t arise with severe symptoms, though chronic deficiencies can cause hypocalcemia (a calcium deficiency disease) or hyperparathyroidism, where the parathyroid glands create a hormone imbalance, according to Medical News Today.
These conditions can lead to bone fragility and osteoporosis; bone pain; muscle twitching, weakness and pain; fatigue and joint stiffness.
If vitamin D deficiency continues for long periods, it may result in autoimmune problems; breast, prostate and colon cancer; neurological diseases; infections; and pregnancy complications.
Vitamin D foods
You probably get the majority of your vitamin D from sunlight exposure, but during the winter, some research suggests that people can benefit from vitamin D supplements.
There aren’t many foods that contain vitamin D, but those that do include:
- Fatty fish such as salmon, mackerel and tuna
- Egg yolks
- Cheese
- Beef liver
- Mushrooms
- Vitamin D-fortified milk, cereal, juice and other foods
