Afrantic e-mail message arrived in my inbox from a friend who was about to become a grandmother. “HELP!” was written in the subject line. The body of her e-mail expressed her fears: “My daughter, Brittany, is seven months pregnant, and she broke her foot. Does she have a problem with her bones? I know you lose bone during pregnancy, do you think she's losing too much?”
I talked directly with Brittany. As it turned out, she had gotten her little toe caught on the leg of her desk and had fallen. She was not worried about anything except the pain. She said her “worrywart” mother had all of the concerns.
The good news is that fractures of toes are not considered to be osteoporotic fractures at any age. Just as Brittany was entering the “waddling stage” of pregnancy, she might have become very uncomfortable and wondered when the pain would go away. However, she did not have to worry about the possibility that her broken toe was a sign of osteoporosis.
Substantial changes do take place in bone metabolism during pregnancy and breastfeeding. Combined, these may result in a loss of 3 to 10 percent of bone. The next question is whether these changes lead to lower bone density and the long-term consequences of fracture. In general, bone loss during and immediately after pregnancy is short-term. Bone density is regained after weaning and resuming menstrual periods.
PREGNANCY
As you would expect, pregnancy increases the body's calcium needs to meet the demands of the growing baby. For women age nineteen and older, the calcium recommendation during pregnancy and breastfeeding is 1,000 mg daily. During pregnancy, it is estimated that 2 to 3 percent of the mother's total body calcium content is transferred to the growing baby. The greatest transfer takes place during the third trimester, when the growing baby's bone development peaks.
By the end of nine months, the baby's skeleton has amassed about 30 grams of calcium. About 80 percent of the calcium is deposited rapidly during the third trimester. This corresponds to a daily calcium demand of about 250 to 300 mg during the third trimester.
How is this demand met? Fortunately, the body has built-in compensation measures. To counteract the calcium loss, the main adaptation in pregnant women is that more calcium is absorbed from the intestine. In this way, a higher percentage of the calcium that is eaten or supplemented is taken up into the blood to meet the demand of the growing baby. A smaller contribution comes from lower levels of calcium loss in the urine. Some calcium may also come from the breakdown of bone. This is minor, so long as expectant mothers are taking enough calcium each day. However, if enough calcium is not provided through dietary and supplemental sources, the mother's skeleton provides the calcium to make up the deficit. The body is a finely tuned machine, as long as you supply what it needs.
In numerous observational studies of postmenopausal women with normal or low bone density, no association was found between their number of pregnancies and bone density or fracture risk. What is actually happening in real time during pregnancy is difficult to study. Since the current best test for measurement of bone density uses low-dose radiation, you cannot use that measurement during pregnancy. The dynamic bone turnover markers have also been evaluated. Interpretation of the data is difficult because the growing baby and the womb contribute to higher levels of bone metabolism.
Women after delivery were found to have 2 to 9 percent lower bone density in comparison with a control group of women of the same age. To get a better idea of what is happening, several clever studies recruited women who were planning a pregnancy. A baseline prepregnancy bone density was compared to a follow-up bone density after delivery. The results were variable based on when the postdelivery bone density was obtained. If the follow-up bone density was done within one to two weeks after delivery, bone density was not different from the prepregnancy measurement. However, when the follow-up bone density was done four to six weeks after delivery, bone density was at the lumbar spine was found to be 3.5 to 4.5 percent lower. These later results might have been influenced by breastfeeding rather than pregnancy.
Although these studies yielded conflicting results that do not entirely answer the question, you can cautiously conclude that there is no net loss of bone density during pregnancy. If there are changes during pregnancy, they do not result in long-term changes in bone density or risk of fracture in postmenopausal women.
Fractures during Pregnancy
In contrast to Brittany's toe fracture, occasionally an apparent fragility fracture (one without significant trauma) may occur during pregnancy or in the first few weeks after delivery. In most instances, the possibility of low bone density before pregnancy cannot be excluded. One's history may reveal an underlying problem that may be a contributing cause, such as the use of steroids. Other considerations include excessive bone breakdown that released calcium from the skeleton because of low dietary calcium intake and vitamin D deficiency during pregnancy. An increased rate of bone turnover is an independent risk factor for fracture. A thorough investigation should be done to look for underlying causes.
POSTPARTUM—AFTER DELIVERY
Effects of Lactation
Calcium demands during breastfeeding are huge. The mechanism for supplying the calcium differs from the mechanism during pregnancy. Hormonal changes ensure a sufficient supply of calcium to the breast milk in most new mothers and, therefore, to the nursing infant. The main source appears to be the mother's skeleton. However, the control of calcium loss from the bone during breastfeeding is not fully understood. Lactation results in the loss of bone. Changes associated with breastfeeding are temporary. The good news is that bone is regained after weaning.
Breastfeeding is associated with a loss of 300 to 400 mg of calcium daily in breast milk. The duration of breastfeeding and the time until the return of regular menstrual periods are both associated with the amount of measurable bone loss. Breastfeeding for six months is associated with a 5 percent bone loss on average, despite the body's attempt to maintain calcium. The calcium drain, in part, explains bone loss during breastfeeding. Nutrition, as well as physical activity, may also play a role in the regulation of bone mass.
The pattern of bone density changes during lactation has been systematically studied by comparing breastfeeding women with women using formula only. Among those in the formula-feeding group, no loss of bone density or a small decrease occurred in the first three months. After that, there was a general increase of 1 to 3 percent over twelve months postpartum. For breastfeeding women, the skeletal site and amount of bone loss varied.
One study showed a redistribution of the bone density in the hip. The neck region lost bone density while another area, the trochanter, gained bone density. Despite the changes that occur during breastfeeding, in the end, no differences were seen between those who breastfed and those who did not. There is no evidence that the duration of lactation has a major effect on bone density. Bone density appears to be restored by approximately six months after stopping breastfeeding. The research data supports the observation that lactation is not associated with increased fractures in later life.
Resumption of Periods
In general, formula-feeding women resume menstruation within three months. For breastfeeding women, the duration of lactation is associated with restarting menstrual periods. When one breast-feeds for less than six months, periods occur close to or slightly after stopping lactation. If one breast feeds for longer than six months, menstruation tends to return before the end of lactation. The resumption of normal hormonal status is thought to contribute to bone density gains.
Timing between Successive Pregnancies
In the case of “Irish Twins”—that is, two babies born in one year—the recovery of bone density is a question. It is not known whether the gain in bone density observed after weaning or resuming menstrual periods can occur if one becomes pregnant before or shortly after weaning. Closely spaced pregnancies might have the potential for long-term effects.
HOW MUCH VITAMIN D?
A physician colleague shared her good news with me. Finally, after multiple attempts, she was pregnant at the tender age of forty-two. She had been in tune with calcium and vitamin D requirements, but later was surprised by her lab results. She told me, “My OB (obstetrician) checked my vitamin D level, and it was only 21. I had been taking 1,000 international units a day and thought that was enough.” Her vitamin D level needed to be a minimum of 30 ng/ml.
Another friend told me that her OB instructed her to stop taking her extra vitamin D supplement of 1,000 IU and to take only the recommended prenatal vitamins. “Was a vitamin D level measured?” I inquired. “No,” she said. “How much D is in your prenatal vitamins?” I asked. She replied, “400 IU.”
Since prenatal nutrition is definitely not within the scope of a geriatrician's expertise, our conversation spurred me on to further investigation. I headed to a local drugstore to inspect the prenatal vitamins. The standard vitamin D content was 400 IU of cholecalciferol, which is vitamin D3. But is that enough? One condition OB/GYNs fastidiously monitor for is pre-eclampsia, which is associated with low levels of vitamin D.
I was curious about what OB/GYNs did as part of their routine practice. So I conducted my own survey, asking twelve physicians from various parts of the country, “What laboratory tests do you order for your pregnant patients?” Granted, it was not a “scientific survey,” but in my small sample, only once did an OB/GYN mention checking vitamin D levels of patients.
My colleague's experience points out that you cannot know how much vitamin D to take without actually having your level measured. You may think you are getting “enough,” but so many variables come into play. Vitamin D is essential for calcium absorption from the intestine. Older studies that looked at pregnancy focused primarily on calcium supplementation and did not take into account vitamin D.
At the Medical University of South Carolina, researcher Dr. Bruce Hollis and neonatologist Dr. Carol Wagner are changing that. In almost five hundred newly pregnant women of three ethnicities (African American, Hispanic, and Caucasian), they found that 82 percent had vitamin D levels less than 32 ng/ml. African American women had the lowest vitamin D levels, with an average of 15.5 ng/ml. In general, women in their first pregnancy were most likely to have low vitamin D levels, pointing out the need for education of new mothers-to-be.
In addition, Doctors Hollis and Wagner are conducting intervention studies of pregnant and breastfeeding women. In one completed study, the women were assigned randomly to three different daily doses of vitamin D supplementation: 400 or 2,000 or 4,000 IU. The 4,000 IU dose, which is about seven times the recommended daily dose of 600 IU, yielded an average vitamin D level of 50 ng/ml. Those taking the 2,000 IU dose had a vitamin D level of 40 ng/ml on average and those taking 400 IU reached an average level of 29 ng/ml. Clearly, ten times the 400 IU dose did not result in ten times the vitamin D level. This points out that larger doses of vitamin D may be required to bring up the vitamin D level to over 30 ng/ml, which is considered the target level.
Higher vitamin D levels were associated with lower numbers of infections and preterm births. I inquired whether their study showed a reduction in preeclampsia, as suggested by cross-sectional studies. Dr. Hollis said, “We saw it trend down but it was not significant. However, when we lumped the complications of pregnancy (pre-eclampsia, gestational diabetes, and blood pressure) together, then it was significantly reduced.”
How much vitamin D is enough? Again, for bone health and nourishing the growing baby, mothers' vitamin D levels need to be at a minimum of 30 ng/ml. Even higher levels may provide more protection and further reduce the likelihood of potential problems in pregnancy. To help more fully answer the question, additional clinical trials are underway using different amounts of vitamin D supplements during pregnancy and breastfeeding.
INFANTS
The American Academy of Pediatrics' latest recommendation from 2008 is to give all breastfed infants 400 IU of supplemental vitamin D daily. The updated 2010 Dietary Reference Intakes for Vitamin D by the Institute of Medicine concurred with the daily intake of 400 IU for infants up to twelve months of age. Infant formulas contain vitamin D in the amount of 400 IU per liter. Supplementation for exclusively formula-fed babies is not needed. However, it is still a need if the baby is fed a combination of formula and breast milk.
One small, six-month study done at the Medical University of South Carolina showed that infants could achieve high enough vitamin D levels exclusively through breastfeeding; but it took supplementation of 6,400 IU of vitamin D each day by the mothers. Their vitamin D levels ranged around the 50 ng/ml level and the vitamin D content of their breast milk increased eightfold from the start of the study.
Vitamin D is a basic requirement for the growing skeleton. Researchers in England looked at bone density in a huge study of almost seven thousand tenyear-old children. Local weather information was used to estimate the mothers' ultraviolet light exposure during the last trimester of pregnancy. Children of mothers whose last trimester occurred during sunny months tended to have larger bones than mothers with less sun exposure. Their research suggests that expectant mothers' vitamin D levels during the time of greatest prenatal bone growth may have lasting effects on children's later bone development. If the benefits persist into adulthood, the researchers concluded, mothers' vitamin D levels during pregnancy might affect their children's bone health into old age.
It is not clear what role vitamin D may play in the long-term prevention of other diseases beyond bone health and in establishing lifelong health. This is an area of hot debate and active research. Just ensure that you and your children or grandchildren have adequate vitamin D intakes. At least be vigilant during the part of the year when there is not enough sunshine for the body to produce its own vitamin D.
Back to the frantic query regarding Brittany's broken toe: Her mother was worried that she had osteoporosis. Major fractures during pregnancy have been reported but they are rare. Brittany was just starting her third trimester, the period of greatest calcium demand. Since her toe fracture was quite painful, she had a built-in reminder about bone health.
If you, a family member, or a friend are planning to become pregnant, the best advice is to start with good nutrition, an adequate vitamin D blood level above 30 ng/ml, 1,000 mg of calcium daily between diet and supplements, and regular exercise. Even better: All of these measures may help conception, too!
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The Bare Bones
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