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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Higher solar UVB during first trimester of pregnancy associated with better fetal development

A study in Greece found that babies born in winter and autumn had higher birth weight, longer gestational age, and two years longer life expectancy than those born in spring or summer [Flouris et al., 2009]. While the author thought the effect was due to environmental temperature, an earlier study from Australia contradicts the hypothesis. It found no effect in temperature change, but rather an effect in sun exposure during the first trimester, resulting in higher birth weights [Tustin et al., 2004].

In the absence of sunlight, vitamin D supplementation should be encouraged. Bruce Hollis and colleagues recently showed that pregnant women can take 4000 IU/d vitamin D3 with no adverse effects [Hollis et al., 2011]. He recommends 4000 IU/d vitamin D3 during pregnancy and lactation [Hollis and Wagner, 2011].

Birth weight 3272 g in winter; 3249 g in autumn; 3145 g in spring; 3147 in summer Flouris, 2009
Gestational age 38.87 wks in winter; 38.82 wks in autumn; 38.19 wks in spring and summer Flouris, 2009
Longevity 76.05 yrs in winter; 76.03 yrs in autumn; 73.93 yrs in summer; 73.72 yrs in spring Flouris, 2009


  1. Flouris AD, Spiropoulos Y, Sakellariou GJ, Koutedakis Y. Effect of seasonal programming on fetal development and longevity: links with environmental temperature. Am J Hum Biol. 2009 Mar-Apr;21(2):214-6.
  2. Hollis BW, Johnson D, Hulsey TC, Ebeling M, Wagner CL. Vitamin D supplementation during pregnancy: double-blind, randomized clinical trial of safety and effectiveness. J Bone Miner Res. 2011 Oct;26(10):2341-57.
  3. Hollis BW, Wagner CL. Vitamin D requirements and supplementation during pregnancy. Curr Opin Endocrinol Diabetes Obes. 2011 Dec;18(6):371-5.
  4. Tustin K, Gross J, Hayne H. Maternal exposure to first-trimester sunshine is associated with increased birth weight in human infants. Dev Psychobiol. 2004 Dec;45(4):221-30.

  About: Dr William Grant

Dr. William Grant is an epidemiologist and founder of the nonprofit organization Sunlight, Nutrition and Health Research Center (SUNARC). He has written over 140 peer-reviewed articles and editorials on vitamin D and health. Dr. Grant is the Science Director of the Vitamin D Council and also serves on their Board. He holds a Ph.D. in Physics from UC Berkeley.

One Response to Higher solar UVB during first trimester of pregnancy associated with better fetal development

  1. very interesting – thanki you Bill, Oliver Gillie