CLINIC: Marathoning with a Thyroid Condition

Tue, 6 Dec. 2011 - 12:06 a.m. MT
Credit: ARA Staff - American Running Association


QUESTION:
My question concerns a possible link between my hypothyroid condition and marathon performance. My goal the past two years has been to run a Boston qualifying time of 4:00 (age 60-64). In the early 1980s, as I turned 40, I ran three sub-3:10 marathons (the master’s standard at the time) and ran Boston in 1984. After a decade off, I had no trouble running two sub-3:30 marathons (age 50-54) in 1994 and 1995 to qualify for the
100th running of the marathon in 1996.
 
My goal of qualifying for and running a third Boston Marathon in a third decade has proved elusive. In 2004, I started the Milwaukee Lakefront Marathon, but dropped out after 21 miles, then entered the Grand Rapids Marathon four weeks later. I posted a
4:03:58. In both cases I ran at a comfortable 9:05 pace for 12 miles, then died. The struggle in the 13th mile has become more like what I would not encounter until 16-18 miles in previous decades.
 
About seven years ago, I began taking a hypothyroid medication. I started with Levoxyl and switched to the generic levothyroxine in June. For all these years, the dosage has
been 10 micrograms. My internist tests for TSH each year. In June 2004 it was 5.15; last June, 5.084. My question: Could my dramatic, premature falloff be linked to my hypothyroid condition? I understand the medication is used for maintenance and there shouldn’t be a wide swing even for a missed dosage (which doesn’t happen),
but might there be a cumulative effect over the weeks of the longer runs and harder track workouts?
 
I am 63 years old, began jogging in 1978 and got serious about running and entered my first races in 1981. That year, in Chicago, I ran a 3:22 first marathon. My concession to age is running four days a week, with a base of two 4-milers and two 6-milers. For race training, one 6-miler is extended and, most weeks, the other is replaced by speed. I keep to two easy 4-milers. I crosstrain once or twice a week. My weight has edged up a little: from about 152 to about 165, but I’m no more than five pounds heavier that I was in
the mid-1990s. I take the thyroid medication with a low-dose aspirin and, during summer months, Claritin.
 
Some websites address general questions about hypothyroidism and running, but I have not found any that address a possible relationship between my condition and
the rigors of a marathon training cycle.
 
Philip Lachney
Chicago, IL
 
ANSWER:
Your TSH is at the upper end of the normal range (at least in most labs), so there is probably room to increase your thyroid replacement slightly (by 12.5 to 25 micrograms), followed by a repeat TSH in 3 months. If it has not decreased below your lab's lower limit of normal, your replacement dose may be more optimal.
 
In addition, though small variations in the amount of active thyroid hormone in each pill are probably not significant, some generic brands of levothyroxine are not considered reliably potent. I would suggest using the brand name Levoxyl for your replacement (it has the most consistent potency data).
 
Whether this minor thyroid abnormality is the reason for your relative decline in performance is uncertain, but these small changes are easy to accomplish and will allow you to test whether the thyroid is the culprit.
 
William Simpson, MD

ANSWER:
 There are multiple factors which may be affecting your marathon performance. First of all, performance decreases with age. Training will slow the rate of decline, but will not stop it.
 
Hypothyroidism can negatively impact performance, though on medications, this should be a minimal/negligible impact. Your TSH is at the upper end of normal limits (a high level is consistent with hypothyroidism); too much thyroid replacement can cause a number of medical problems. Your TSH levels are consistent over time, though levels do need to continue to be monitored. Adjusting the medication dosage so that your TSH is on the low side of normal would probably not have a significant impact on training and could cause side effects.
 
I think that you need to look at your training schedule and racing pace. It looks like your fastest miles are at the start of the race; most runners perform best with even or negative splits. Are you using too much energy (for your level of training) early in the race and paying for it in the middle of the race? Possibly incorporating a medium length run at planned marathon pace in your schedule will be helpful; start at 6 miles and gradually increase to 12 miles. This could replace your speedwork. Make sure that there is sufficient recovery between this and your long run. You might also consider working with a coach to tailor a training program to your needs.
 
Cathy Fieseler, MD
 
(RUNNING & FITNEWS®  February / March 2007 • Volume 25, Number 2)
 
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