Scurvy, is a disease that claimed the lives of many sailors in the 17th, 18th and even the 19th century. The common cold makes its rounds every fall and winter.

These are two very different ailments with one simple remedy – vitamin C. Vitamin C also helps prevent heart disease, high blood pressure, osteoarthritis, asthma, and even cancer.

Sadly, there’s one little snag in this happy tale. That’s the gene, SLC23A1, which controls vitamin C levels in the body.

People can’t make it

Vitamin C, also known as ascorbic acid, is an essential nutrient that must be obtained from our diet. Humans, unlike most animals, can’t make it in our bodies.

This nutrient has a diverse range of functions, including the production of collagen (an essential component of connective tissues and important for wound healing), the synthesis of neurotransmitters (chemical messengers in the brain), stimulation of immune function, and the absorption of non-heme iron.

Most importantly, vitamin C acts as an antioxidant. Antioxidants are substances responsible for removing toxins, called reactive oxygen species (ROS). ROS are a natural byproduct of energy generation in the body. Vitamin C lowers ROS levels, and also plays a role in the regeneration of other antioxidants (e.g. vitamin E), doubling up its protective effects.

Taking it in

To absorb vitamin C into our cells, we need protein “transporters” on the cell surface. The SLC23A1 gene encodes one of these transporters, called solute carrier family 23 member 1.

Genetic variants (small changes in the DNA) affect the activity of this transporter protein. One variant, called rs33972313 A, is associated with reduced levels of vitamin C. This altered transporter is much less efficient at absorbing vitamin C and distributing it around the body.

Symptoms of deficiency

Scurvy is the ultimate consequence of long-term vitamin C deficiency. It can be a deadly disease when left untreated. Symptoms include bleeding under the skin, poor wound healing, bruising easily, loss of hair and teeth, joint pain, and swelling.

Many of these symptoms can be linked back to weakening of connective tissues and organs that contain collagen, like the skin, bones and heart. Furthermore, excessive bleeding associated with scurvy can lead to iron deficiency anemia.

Thankfully, it’s a rare condition today, particularly in developed countries. Just one orange gives you more than enough vitamin C to meet your daily requirement. For recommended dietary allowances and foods high in vitamin C, refer to the tables at the end of this article.

Pay attention to your supplement intake 

Vitamin C toxicity is also quite rare. Extremely high doses can give you headaches, insomnia, kidney stones and stomach upsets, leading to diarrhea, nausea, vomiting, heartburn, bloating, and cramps.

However, this vitamin is water-soluble, which means that any excess vitamin C is eliminated from the body in urine. So unless you plan on eating more than 25 oranges or 10 cups of red peppers a day, it’s highly unlikely that you will ever reach the upper limit of 2,000 milligrams per day.

But if you are taking concentrated vitamin C supplements to ward off those winter colds, you should keep track of how much you are taking. Tolerable upper intake levels for each age group are shown at the end of this article.

Do you need more vitamin C?

Vitamin C really is a super nutrient. It can lower our risk of disease, and higher levels are indicative of overall good health. Unfortunately, genes like SLC23A1, which influence vitamin C levels, can put you at a disadvantage.

But when you know the risk, you can mitigate it. The SLC23A1 variant is included in the DNA Nutrition Test. When life gives you lemons, or bad genes in this case, choose to make lemonade, and for the sake of your health, drink much more of it.

Recommended dietary allowances for vitamin C

Recommended dietary allowances are shown in milligrams (mg). Adequate intake shown for infants from birth to 12 months is equivalent to the mean intake of vitamin C in healthy, breastfed infants.

Individuals who smoke require 35 mg/day more than non-smokers.

Selected foods sources of vitamin C

The Daily Value (DV) for vitamin C is 60 mg for adults and children age 4 and older. The U.S. Food and Drug Administration (FDA) developed DV to help consumers compare the nutrient contents of products within the context of a total diet.

Tolerable upper intake levels for vitamin C

These upper limits apply to both food and supplement intakes, but do not apply to individuals receiving vitamin C for medical treatment under the care of a physician.

For infants from birth to 12 months, breast milk, formula and food should be the only sources of vitamin C.

Recommended dietary allowances, food sources and tolerable upper limits are obtained from the Vitamin C Fact Sheet for Health Professionals (National Institutes of Health).