Up in Smoke3

In this case, it's better to buy it at the store than to squeeze it yourself. That's because the vitamin D comes not from the oranges themselves, but from the makers who add it to the juice at the factory. Look for the words "fortified with vitamin D" on the label. You get about 2.5 mcg for each cup.

Most adults need about 15 micrograms (mcg) a day. This goes down to 10 mcg in infants and up to 20 mcg in adults 71 or older. On labels, you may see vitamin D amounts listed in international units (IU). A single microgram is equal to 40 international units.

It's important for your bones, blood cells, and immune system -- your body's defense against germs. You get most of your vitamin D from sunlight on your skin. Just a few minutes a day on your hands and face should do the trick. But you can also get it from food. If you're homebound, sick, or older, you might not get enough vitamin D. Talk to your doctor if you think your levels are low.

Before the 1700s, this potentially deadly disease used to be a huge problem for sailors. Today, it's relatively rare but possible if you get only 10 mg/day of vitamin C or less. People with scurvy also have problems such as loose teeth, cracked fingernails, joint pain, brittle bones, and corkscrew body hair. When you boost vitamin C, symptoms start getting better in a day, and usually it's cured within 3 months.

If you have age-related macular degeneration (AMD), it may get worse faster without vitamin C and other antioxidants and certain minerals. Getting enough vitamin C from foods might help prevent cataracts, but we need more research to understand that relationship better.

Since vitamin C has several jobs related to your immune system, it shouldn't surprise you to learn you're more likely to get sick and may have a harder time recovering. There's some evidence that vitamin C can help protect you from illness such as pneumonia and bladder infections. It may even lower your odds of heart disease and some types of cancer.

In a very small study, 6 of the 7 men who had low levels of vitamin C said they felt tired and irritable. That suggests a link, though other things could be playing a role. Another study of 141 office workers found that giving them vitamin C made them feel less tired within 2 hours, especially if their level was lower to start with. Then the effect lasted for the rest of the day.

People who eat a healthy diet with plenty of vitamin C may have smoother, softer skin. One possible reason: Because vitamin C is an antioxidant, it can help protect your skin from free radicals. These break down oils, proteins, and even DNA.

Early research has found a link between low levels of vitamin C and higher amounts of body fat, especially belly fat. This vitamin may also play a role in how well your body burns fat for energy.