The ongoing health crisis has gotten people seeking food and vitamin supplements believed to boost immunity, the most popular of which is vitamin C—both found in capsule format and whole food items like fruits and vegetables.
While vitamin C does contribute to immune defense by “supporting various cellular functions of both the innate and adaptive immune system,” according to a study by Anitra Carr and Silvia Maggini, relying solely on vitamin C and taking more than the body requires are not recommended.
For reference: the Harvard Medical School says the Recommended Dietary Allowance (RDA) of vitamin C for men is only 90 milligrams per day, and 75 milligrams for women. In an interview with Manila Standard, infectious disease specialist Dr. Marion Kwek said taking one 500mg capsule of vitamin C was more than enough per day.
So what are these two other nutrients experts say are essential in fighting illnesses?
They are vitamin D and zinc.
“Even mild to moderate degrees of zinc deficiency can impair immune function and make you susceptible to pneumonia and other diseases. Meanwhile, vitamin D or what we call the ‘sunshine vitamin’ is critical to bone health, as well as infection and inflammation control,” says Dr. Mercedita Macalintal, a clinical nutrition support specialist at Makati Medical Center.
What do they do
A study by researchers from Ohio State University a few years ago revealed zinc reduced the severity and possibly shortened the duration of the common colds in humans. Recent findings by researchers from Spain during the ongoing pandemic, meanwhile, found that people with lower blood levels of zinc admitted to hospital with COVID-19 “tended to fare worse than those with healthier levels.”
Dr. Macalintal explains that zinc is responsible for the proper functioning of the immune system by removing harmful free radicals, repairing cells, and replicating them. It is also in charge of the catalytic activity of more than 100 enzymes, synthesis of genetic materials, and maintenance of cell integration. The nutrition expert adds the nutrient is also essential for growth and development.
Zinc deficiency may result in poor immune system function, slow wound healing, diminished sense of taste and smell, appetite loss, diarrhea, and skin rashes around the nose, mouth, and anus.
Dr. Macalintal notes that it is also associated with spontaneous abortion, congenital malformation, low birth weight, intrauterine growth retardation, and possible complications during labor and deliveries for pregnant women.
Vitamin D, on the other hand, is associated with modulating “the innate and adaptive immune responses,” according to Dr. Cynthia Aranow.
“Having adequate vitamin D can also help improve your mood, especially in these challenging times. Vitamin D deficiency may increase your risk of depression and may even affect cognitive function and brain health,” adds Dr. Macalintal.
With most of us staying home to curb the spread of coronavirus, Dr. Macalintal warns that we could be more prone to vitamin D deficiency, which she says may affect how our body fights acute respiratory infection and prevents chronic illnesses like coronary heart disease, diabetes, and certain cancers.
Several factors can lead to vitamin D deficiency like age (older adults are less capable of producing vitamin D compared to young adult), skin pigmentation due to UV penetration on the skin, obesity, and certain forms of malabsorption disorders and too much use of blocking creams.
Dr. Macalintal lists down some signs and symptoms of vitamin D deficiency: frequent colds, flu, and other respiratory infections; muscle, bone, and back pain; skeletal deformities; slow wound healing; severe hair loss; and irritability, especially in children because of bone pains.
Where to get them
The body cannot produce or store zinc, which means it has to be obtained from diet or supplements.
“To prevent zinc deficiency and the problems that go with it, you need to supplement your body with it through the food that you take,” reiterates Dr. Macalintal.
But again, more is not better in this case. The body’s zinc requirement depends on age and gender; according to the latest Recommended Energy Intakes (RENI) by the Food and Nutrition Research Institute (FNRI), an adult woman only needs 5mg per day, while an adult male will require 7mg per day.
Pregnant or lactating women, meanwhile, will need 12 milligrams of zinc. Children should take at least 2 milligrams and up to 10mg, depending on their age and gender.
Food items high in zinc include oysters (74mg in every 3 ounces), roast beef (7mg in 3 ounces), and crab (6.5mg in 3 ounces), according to a medically reviewed article on drugs.com. Other food sources, Dr. Macalintal says, are lobsters, pork, beans, nuts, whole grains like oatmeal and brown rice, dairy products, and some green leafy vegetables.
Vitamin D, meanwhile, can be produced by our skin “when we get our daily dose of sunlight.” But if you can’t spend some healthy time under the sun, Dr. Macalintal says it can be obtained from the food we eat.
“You can still increase the amount of vitamin D in your body by eating fatty fish, egg yolks, cheese, and beef liver. Taking vitamin D supplements can also help.”
The RDA for vitamin D also varies depending on age. According to the National Institutes of Health, daily intake for children and adolescents (0-18 years old) is 10-15 micrograms (mcg) or 400-600 IU (international units); 15mcg (600 IU) for 19-70 years old; and 20 mcg (800 IU) for 70 and above.