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Medical Myths Medical Myths

Can We Predict Height?

September 25, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Are you happy with your height? Did you ever wish you were taller or shorter than you are? Some people dream of being a professional basketball player or a fashion model, if only they were taller; others wish they were shorter because they literally stand out in a crowd. But, more often than not, when it comes to one’s height we look much more like our parents than any sports hero or movie star.

Questions and misconceptions are common about what factors determine human height. Can it be predicted in advance? Do large feet really predict exceptionally tall stature? Does coffee stunt your growth? Read on for answers to these and other questions about why you are as tall as you are — no taller, no shorter.

What Determines Height?

One’s ultimate height is determined by a complex interaction of many factors including nutrition, genes, and overall health. Growth rates vary over a lifetime:

  • From infancy, when average length is 20 inches, to age 2 there is initially rapid growth, then slowing, with about 14 inches in height added.
  • From age 2 to puberty there is slow, steady growth at about 2½ inches per year.
  • As one enters puberty, a growth spurt of 3 to 5 inches in a year is common.
  • By ages 40 to 50, height actually may begin slowly to decline, even in healthy adults.

A major determinant of height is how long the longest bones become, such as the femur (in the upper leg), tibia and fibula (in the lower leg). Long bones have "growth plates," areas toward the ends that have a space allowing elongation. When growth is complete (generally by age 17 or so), the growth plates close and the bone cannot get any longer.

A number of hormones are involved with normal development and ultimate height, including the growth spurt that occurs around the time of puberty. These hormones include (the appropriately named) growth hormone, thyroid hormone, cortisol and the sex hormones (estrogen and testosterone). During the pubertal growth spurt, the hands and feet enlarge before the long bones, so that for many, the first indication that rapid growth is about to begin is an increase in shoe size.

As you may have noticed, gender has a significant effect on height: The growth spurt around the time of puberty occurs two years earlier in girls when compared with boys, but the boys tend to be taller when it begins. Most of the average height difference between adult men and women (about 5 inches) relates to the greater growth of boys during the adolescent growth spurt and the greater height achieved prior to that growth spurt (even though girls tend to start their growth spurt sooner).

Genes play an important role in determining height even beyond the fact that they determine gender — under the best of circumstances, with good nutrition and overall health, it is one’s genes that have the biggest effect on ultimate height. Siblings in similar environments who eat similar diets have different heights at least in part because the mix of genes from their parents is different in each child. And genetic abnormalities may stunt growth. For example, persons with Down syndrome are nearly always much shorter than their genetically normal siblings. Similarly, certain ethnic groups tend to be taller (or shorter) due to genetic differences.

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Can Height Be Predicted?

Genes, nutrition, and overall health have their effects right from the beginning. Rather predictably, we achieve about half of our adult height by age 2. So one way to predict ultimate height is simply to double the height achieved by the second birthday. Other ways to predict height take information from childhood growth charts (see below), your parents’ height, and a reading of your "bone age." Bone age is assessed by X-rays that indicate how much development has already occurred in the skeleton and how much more is possible. If the growth plates are still open,for example, more growth is likely. The closer you are to final height (by virtue of your age or the finding of closed growth plates on X-rays), the better these formulas predict height.

The observation that family members tend to be of similar stature is born out by formulas designed to predict height. One commonly quoted formula uses parental height and gender to predict adult height (in inches) as follows:

   For men: (height of mother + height of father + 5)/2
   For women: (height of mother + height of father – 5)/2

If you know your parents’ heights, see if this formula predicts yours well; for most people, this will accurately predict your height within 2 or 3 inches.

All of these methods can only approximate ultimate height; they cannot predict with precision. In addition, formulas and growth charts to predict height are based on large numbers of normal children and do not perform well in predicting the ultimate height of an individual child who is unusually short or tall, has been ill, or has a genetic disorder. For some conditions, including Down syndrome, separate growth charts have been developed.

Height (or, more accurately, length) at birth does not predict ultimate height well; the same goes for foot size. Although a sudden increase in shoe size heralds the beginning of rapid growth around the time of puberty, foot size itself is a poor predictor of ultimate height.

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Diet and Height

The most powerful effect of diet is seen in malnourished children who experience delayed development and short stature. A well-balanced and appropriate diet maintained throughout childhood in the absence of illness will probably lead to the maximum height possible; beyond that, there is no evidence that enriching a diet with (or avoiding) a particular food will alter the height one is otherwise destined to reach. For example, there is no compelling evidence that coffee or caffeinated beverages stunt growth.

In recent years, controversy has swirled around the intake of fruit juice drinks. Some studies found that among those children with the highest intake (more than 12 fluid ounces per day), obesity and shorter stature were more common. More recent studies refute that claim.

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Conditions Affecting Height

Most children and adults who are considered short have no specific disease. They have short parents (that is, they have a reduced genetic potential for tallness) or they have delayed growth and will eventually have normal adult height. Premature infants or other very small infants sometimes never completely "catch up," and although they are healthy, their adult height is shorter than would be expected based on parental height.

However, any serious illness (and sometimes the medications used to treat it) can affect development, including height. Examples include kidney failure, cystic fibrosis, and intestinal disorders that reduce absorption of nutrients. Diabetes that starts during childhood (usually type 1) used to be a common cause of and short stature in children, but early recognition and treatment has reduced this effect on height.

Other common examples of diseases that affect height include:

  • Normal aging and osteoporosis — People tend to lose height as they age. This is mostly related to osteoporosis and reduced water content in the disks (so that the distance between each vertebra is reduced). On average, women lose about 2 inches over their lifetime, while men lose about 1 inch.
  • Hypothyroidism — A reduction in the normal amount of thyroid hormone during childhood typically leads to short stature, among other problems, such as poor school performance, fatigue, constipation and cold intolerance. Another form, congenital hypothyroidism, is present at birth and if not detected (usually by routine blood tests), feeding problems, lethargy, an enlarged tongue and mental retardation may follow.
  • Growth hormone abnormalities — Children with reduced growth hormone have a much reduced growth spurt around the time of puberty, leading to short stature. Conversely, if excessive growth hormone is present before growth plates close, "giantism" — a dramatic increase in height — may follow.
  • Hypogonadism — This condition is marked by a reduction in sex hormones, including testosterone and estrogen. Affected persons may have little or no growth spurt at the time puberty is expected.
  • Arthritis — When children develop joint inflammation, growth of the nearby bones are often affected. If it occurs before age 3, the affected limb may be longer than expected, but if it occurs after age 9, the growth plates may close earlier than expected, leading to reduced leg length. There is often a more generalized growth reduction in children with active arthritis.
  • Corticosteroid therapy — These powerful anti-inflammatory medications can affect height through their effects on bone development. They may be prescribed for a number of conditions including Crohn’s disease, ulcerative colitis, asthma or arthritis, although usually viewed as a last resort. If taken during childhood for prolonged periods, growth retardation is common.
  • Poor nutrition — If infants or children do not have adequate access to a balanced diet, or if intake is inadequate for another reason (such as depression or fear of obesity), adult height may be shorter than expected.

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The Bottom Line

If you are like most healthy people, your height is similar to that of your parents, closer to your father’s if you are male, closer to your mother’s if you are female. Once you have reached your adult height, there’s not much you can do about it, but you may be able to prevent some of the loss of height during aging. Talk with your doctor (or your child’s pediatrician) if you have concerns about your height or that of your child. If you don’t like how tall you are, don’t blame the coffee or the fruit juice — it’s probably more appropriate to blame your parents. But remember Abraham Lincoln's response when asked how long a person's legs should be: "Long enough to reach the ground."

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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