Changes in dietary vitamin intakes among women: Study

“[I]t is necessary to understand how women’s dietary patterns change over time among those who are pregnant and who may become pregnant, to better improve the nutritional status for these populations,” wrote researchers from the United States, United Kingdom and the Netherlands. “By identifying these nutrient gaps and trends in inadequate intake in this at-risk population, scientific, health care and regulatory communities may be better poised to adopt recommendations to improve nutrient intake.”

Prior data has shown that over 40% of pregnant women did not meet estimated average requirements for magnesium, vitamin D and E. While there is no established dietary requirement for DHA for pregnant women, experts agree it should be 200 mg/d; prior studies reported 95% of women consumed less than this daily. Non-pregnant women have a similar inadequate intake of vitamins.

Study details

The study, a cross-sectional analysis of 20 years of NHANES data, included both pregnant and non-pregnant women between the ages of 20 and 44. The complex, multi-stage probability sampling was carried out from 1999 to 2018. Through dietary recalls, the data illustrates macro and micronutrient intake for women over 24-hour time periods. Dietary supplements consumed up to 30 days prior to the recall were recorded as well. Of the total sample size, 1,392 women were pregnant and 9,737 were not.

Dietary carbohydrate intake decreased for both pregnant and non-pregnant women. For pregnant women, this was from 2013 to 2018 and for non-pregnant women from 1999 to 2018. Despite a decrease in carbohydrate intake, dietary fiber intake increased.

While the carbohydrate decrease was not associated with an increased intake in protein or fat, the energy contribution from dietary fat increased for both groups.

“Moreover, the change in the proportion of women whose dietary fat intake was above the AMDR increased by 23.2 percentage points […] for pregnant women and 33.4 pp […] for non-pregnant women,” the researchers wrote.

The researchers noted that although vitamin C is not considered a nutrient of public concern, their analysis showed that the risk for inadequate intake of vitamin C for women who are pregnant has increased three fold from 1999-2000 and 2017-2018. For non-pregnant women, this increased by 40%.

“The decreases in intake appear to be largely associated with decreased consumption from foods and beverages alone,” they stated.

Regarding DHA, the study found intake was relatively consistent over the 20 years, but pregnant women who consumed at least 250 mg of DHA and EPA increased significantly. The increase was associated mainly with supplementation rather than diet.

“Consistent with previous studies, these analyses showed that most women (>90%) do not consume the recommended 250 mg/d of combined DHA and EPA, which also suggests that most women are not meeting the recommendation for 200 mg/d of DHA alone,” the researchers wrote.

Dietary supplementation trended downward slightly for pregnant women and slightly up for non-pregnant women for the latter decade of the study.

"This study suggests that decreases in vitamin A, vitamin C, and iron intake can compromise nutritional adequacy among women and could, in turn, affect maternal and fetal outcomes," the researchers wrote.

Source: JAMA Network Open ​2024;7(10)
doi: 10.1001/jamanetworkopen.2024.38460​
“Macronutrient and Micronutrient Intake Among US Women Aged 20 to 44 Years”
Authors: Miketinas, D., et al.