What to Know About Vitamin D

Vitamin D is unusual among vitamins. The body can make it when sunlight reaches the skin, few foods contain it naturally, and low levels are common in many parts of the world. It is essential for healthy bones, and it is also one of the nutrients that can cause harm in excess.

What vitamin D does

Vitamin D helps the body absorb calcium, one of the main building blocks of bone. Without enough, bones can become thin, brittle or soft. Muscles need it to move, nerves need it to carry messages, and the immune system needs it to fight off bacteria and viruses.

Where it comes from

Sunlight

Skin makes vitamin D when exposed to ultraviolet B rays. The amount varies with season, latitude, time of day, cloud cover, skin tone, age and sunscreen use. Because UV also causes skin cancer, health authorities do not recommend unprotected sun exposure as the way to get vitamin D.

Food

Few foods contain much naturally. The best sources are fatty fish, such as salmon, trout, tuna and mackerel, and fish liver oils. Egg yolks, cheese and beef liver have small amounts. In the United States, most milk and many breakfast cereals and plant-based drinks are fortified.

Supplements

Supplements contain vitamin D2 or vitamin D3. Both raise blood levels, although D3 may raise them higher and for longer. Our Vitamin D3 1000 IU softgels provide 25 micrograms each.

How much you need

Recommended daily amounts from the NIH Office of Dietary Supplements:

• Ages 1 to 70: 15 micrograms (600 IU)
• Ages 71 and over: 20 micrograms (800 IU)
• Pregnancy and breastfeeding: 15 micrograms (600 IU)

One microgram equals 40 IU.

Who is more likely to have low levels

• Older adults, whose skin makes vitamin D less efficiently
• People who seldom go outdoors or who cover most of their skin
• People with darker skin, which makes less vitamin D from sunlight
• Breastfed infants, because breast milk alone is low in vitamin D
• People with conditions that limit fat absorption
• People with obesity or who have had gastric bypass surgery

Signs of deficiency

In children, severe deficiency causes rickets, in which bones become soft and bend. In adults, it causes osteomalacia, with bone pain and muscle weakness. Long-term shortage contributes to osteoporosis. A blood test for 25-hydroxyvitamin D measures your level; your doctor can advise whether testing is appropriate.

Too much vitamin D

Very high intakes, almost always from supplements, raise calcium in the blood. This can cause nausea, vomiting, muscle weakness, confusion, pain, dehydration and kidney stones, and in extreme cases kidney failure and irregular heartbeat. The adult upper limit is 100 micrograms (4,000 IU) a day. You cannot get too much vitamin D from sunlight, because the skin limits how much it makes.

Interactions

Vitamin D supplements can interact with some medicines, including certain weight-loss drugs, cholesterol-lowering statins, steroids and some diuretics. Check with a pharmacist or doctor if you take regular medication.

Taking it sensibly

• Add up vitamin D from all your supplements, including multivitamins and calcium products.
• Take it with a meal that contains some fat.
• Do not take high doses long term without medical advice.

The bottom line

Vitamin D matters for bones and muscles, and many people get little from food. A modest daily supplement is a common way to top up; high doses are a matter for your doctor. See options in our vitamins and nutrition range.

Sources

1. NIH Office of Dietary Supplements. Vitamin D.
2. NHS. Vitamins and minerals.
3. MedlinePlus. Vitamins.