At one time, sailors aboard ships with no access to fresh fruit often came down with swollen gums and spotty skin – all early signs of scurvy, a potentially lethal disease caused by vitamin C deficiency.
More recently, you may have heard someone say brittle hair or nails is a sign you are lacking something in your diet.
It still holds true that skin, hair, nail and mouth problems can be outward signs of vitamin and mineral deficiencies. However, in the U.S. and other developed countries, "with the exception of iron, few people have true deficiencies that bring on outward symptoms because our food is fortified," said dietician Lauren Graf of Montefiore Medical Center in New York City.
Dr. Tony Nakhla said another exception is vitamin D, which the body produces naturally in response to direct sunlight. Sunblock, which many use religiously to guard against skin cancer, prevents this process from occurring.
Since the 1920s, nutrients have been added to staples like bread, milk and cereal to help Americans meet our daily recommended allowance for vitamins and minerals. Still, people's intake of certain vitamins and minerals can be suboptimal, Graf said.
But will those shortages show up on their outward appearance?
"Deficiency of either vitamin A or beta-carotene can lead to excessive formation of keratin, a skin protein that can clog the pores to produce a goose-bump effect usually most obvious on the back of the upper arm," said Dr. Michael T. Murray, a naturopathic physician and co-author of "The Encyclopedia of Natural Medicine" (Atria, Third Edition, 2012).
Sore or bleeding gums can point to a vitamin C deficiency, "lifeless" hair to a lack of essential fatty acids ("good" fats) and dry, scaly skin to a biotin deficiency, he added.
Brittle or streaked nails are associated with several vitamin and mineral deficiencies, including iron, but that does not mean a person's first stop should be the supplement aisle. "The first thing they need to do is be seen by their dermatologist because the more common cause of these symptoms is nail fungus, which needs to be ruled out or treated," said Nakhla, author of "The Skin Commandments" (Reedy Press, 2011).
Other potential causes or underlying problems could be thyroid disease, renal failure and lung cancer.
Lank hair, scraggly nails and dull skin may indeed be signs of a poor diet, but not necessarily in terms of deficiencies. "People over-associate nail, skin and hair problems with nutritional deficiencies but they are more likely caused by an excess of bad things in processed foods" such as trans fats and additives, Graf said.
The two most concerning deficiencies in America, iron and vitamin D, don't have telltale outward signs.
"A lot of people associate iron deficiency with being tired, weak, fatigued and pale. All of these are symptoms," Graf said, "but it can also cause rapid heart rate and shortness of breath, which people may not realize."
Chronic fatigue and recurrent infections may signal a vitamin D deficiency, but the only way to diagnose it is with a blood test.
While most supplements won't hurt, "many won't help, and in some cases a vitamin excess can be just as bad as a deficiency, or worse," Graf said. "The answer is seldom so simple as popping a pill."
Vitamin D supplements can increase inflammation, while iron overload is especially hard on older adults.
Bottom line: "There's no way to look in the mirror and say, 'I have a vitamin deficiency,'" Nakhla said.
If you suspect you do, see your physician.