Those first few strands of grays on your head are often not a welcome sight. They're a sign that we're getting older, whether they arrive prematurely in our 20s or spare us until we're in our late 30s. But in some instances, gray hair may indicate more than our biological age: It could signal one of these five health issues.

1. Men may have increased risk of heart disease

According to a recent study published by the European Society of Cardiology, gray hair is linked with an increased risk of heart disease in men.
In the study, 545 adult men were divided into groups based on whether or not they had coronary artery disease and how much grey or white hair they had. The amount of grey hair on each man's head was graded on a scale of 1 to 5, with 1 being almost none and 5 being pure white. Scientists also collected data on the men regarding hypertension, diabetes, smoking habits and family medical history.
Researchers found that a hair score of 3 or more "was associated with increased risk of coronary artery disease independent of chronological age and established cardiovascular risk factors," according to the press release. Participants who already had coronary artery disease had "a statistically significant higher hair whitening score and higher coronary artery calcification" than those without it.
"Ageing is an unavoidable coronary risk factor and is associated with dermatological signs that could signal increased risk," said Dr. Irini Samuel, a cardiologist at Cairo University in Egypt. More research is needed, she said, adding: "If our findings are confirmed, standardisation of the scoring system for evaluation of hair greying could be used as a predictor for coronary artery disease."

2. You may have a vitamin deficiency

Woman looking at her gray hairThe '50-50-50' rule of thumb states that at 50 years old, 50 percent of the population has at least 50 percent grey hair. (Photo: cunaplus/Shutterstock)
Before we get into this one, let's back up. Each hair follicle contains pigment (called melanin — the same thing that colors our skin) that gives our hair its color. As we get older, we produce less pigment, resulting in gray hair. Dermatologists usually use the "50-50-50" rule of thumb which states that at 50 years old, 50 percent of the population has at least 50 percent grey hair.
However, some people go gray early. What's early? As WebMD reports: "Typically, white people start going gray in their mid-30s, Asians in their late 30s, and African-Americans in their mid-40s." So early is before those benchmarks, and its those early gray strands that may indicate a nutritional imbalance.
"Low vitamin B12 levels are notorious for causing loss of hair pigment," says Dr. Karthik Krishnamurthy, director of the Dermatology Center's Cosmetic Clinic at Montefiore Medical Center in the Bronx, New York, tells Good Housekeeping. And a 2013 study found low vitamin D3, serum calcium and serum ferritin levels in people who went gray prematurely.
Early gray hair also can be a sign of a problem with your pituitary or thyroid gland, according to WebMD.

3. Your follicles may suffer from 'oxidative stress'

Hair follicles produce small amounts of hydrogen peroxide, a chemical that has been used for decades as an inexpensive way to lighten or bleach hair. However, if a hydrogen peroxide buildup occurs, your hair color may start to fade. As this 2013 study published in the Federation of American Societies for Experimental Biology journal reports:
In a new research report ... people who are going gray develop massive oxidative stress via accumulation of hydrogen peroxide in the hair follicle, which causes our hair to bleach itself from the inside out. Most importantly, the report shows that this massive accumulation of hydrogen peroxide can be remedied with a proprietary treatment ... described as a topical, UVB-activated compound called PC-KUS (a modified pseudocatalase). What's more, the study also shows that the same treatment works for the skin condition, vitiligo.

4. You are (or were) a smoker

A 2013 study published in the Indian Dermatology Online Journal found that smokers are two and half times more likely to develop premature gray hair than people who do not smoke. And smoking can go one step further in damaging your tresses: Certain chemicals in smoke break down in hair cells, which leads to baldness, according to the New York Times.

5. Gray is in your genes

Businessman with gray hairA 2016 study found the exact gene responsible for giving us that salt-and-pepper look. (Photo: Air Images/Shutterstock)
This we know: If your parents or grandparents went gray and did so early, then chances are you will, too. But in a relatively new twist, this 2016 study found the exact gene responsible for gray hair. The study looked at the genomes of more than 6,000 people from Latin America and identified 18 genes that influence hair traits, including IRF4, which previously was known for producing light hair in people of European origin but now is associated with gray hair.
“This is the first time a gene for graying has been identified in humans,” said lead author Dr. Kaustubh Adhikari, a researcher at University College London, in a press release. “As hair grays something happens that causes this gene to produce even lower levels of melanin. Now we can ask more specific functional questions,” Adhikari told Newsweek.
Then again, if you're sporting the salt-and-pepper look these days, it may mean simply that you've accumulated some life experience and earned your stripes — whether you choose to dye them or not.