Summer-Born Children Tend To Be Taller And Stronger

By Margarita Nahapetyan

A new large study suggests that children who are born in late summer or early autumn are more likely to be taller and stronger than those born in spring and winter.

Future mothers-to-be lucky enough to be blooming in the hot months should get enough sun to increase their vitamin D levels just by walking around outside or even sunbathing. But pregnant women whose babies are expected to be born between November and May, should consider taking vitamin D supplements, researchers at Bristol University recommended.

In their project the researchers focused on whether exposure to UVB rays in sunlight in the last three months of pregnancy was related to a child's bone mineral content (BMC), a measure of bone mass. They also were interested whether this connection was due to the effects of vitamin D levels on height, fat or lean mass (muscle weight), or whether BMC was free of these factors.

The Bristol researchers examined the likely sun exposure of the mothers of 7,000 children in the last trimester of their pregnancy. The offspring were measured and underwent X-ray scans at the age of 10, in order to determine their bone density. The results of the project, which lasted for 18 years, showed that children born in the summer and early autumn months, were half a centimeter taller on average, and had nearly 13 sq cm of extra bone area due to increases in bone width, compared with the kids born in winter months.

Any woman who thinks that she can just short-cut the process by sitting on a sun bed in the final weeks of her pregnancy would be doing herself no good. Sun beds emit mainly UVA light, whereas it is natural UVB rays from the sun that trigger vitamin D production. Sun bed users also face well-publicized risks, study spokeswoman Sally Watson, explained. "Perhaps people should not be quite so terrified of the sun. There has been a lot of panic about skin cancer but people do not need to panic about the odd few minutes of exposure. A little controlled English sun is better than none. Or go to the Bahamas!"she said.

Taller people tend to have wider bones but these children had increased bone width "over and above" that accounted for by their extra height, the team found. The scientists said that the increase in bone mass could be associated with higher vitamin D levels, proving one more time that vitamin D is essential for bone-building even in the womb.

Vitamin D, which works together with calcium to build strong bones, is generated by sunlight on the skin. For most people, sunlight is the main source of the vitamin. Vitamin D levels were also measured in the blood of 350 women in the 37th week of pregnancy, and closely mirrored their sun exposure levels.

One of the researchers on the project, Jon Tobias, Professor of Rheumatology at Bristol University, said: "Wider bones are thought to be stronger and less prone to breaking as a result of osteoporosis in later life, so anything that affects early bone development is significant. Pregnant women might consider talking to their doctor about taking vitamin D supplements, particularly if their babies are due between November and May, when sunlight levels are low."

However, while sunlight can increase the levels of vitamin D in the body, there is established evidence that sunbathing and exposure to high levels of the sun's ultraviolet light, pose risk to health. Current guidance from the National Institute for Health and Clinical Excellence (NICE) states that it is important to maintain adequate vitamin D during pregnancy and breastfeeding, and that women pregnant in winter months should take up to ten micrograms of vitamin D a day through supplements.

A 40-year review of research found that a daily dose of Vitamin D could significantly decrease the risk of breast and colon cancer. It also plays a vital role in protecting against heart disease, cancer, diabetes and high blood pressure as well as being essential for bone health. Just 20 minutes in the sun, with the hands, arms and face exposed, is all that is needed to receive daily norm, but it needs to be done on a regular basis. In winter the only way of maintaining levels is by taking cod liver oil or supplements.

The results are the latest to emerge from the Avon Longitudinal Study of Parents and Children (ALSPAC), which enrolled 14,000 pregnant mothers between 1991 and 1992 and has since followed the development of their offspring in "minute detail." The study, also known as Children of the '90s, is funded by the Medical Research Council, the Wellcome Trust and the University of Bristol. It was published in the Journal of Clinical Endocrinology & Metabolism.