Boost Vitamin D in Blacks Living at High Latitudes, Study Indicates

Nancy A. Melville

September 17, 2021

The lower vitamin D levels typically seen in populations residing at higher latitudes with lower sun exposure extend to people of African-Caribbean descent. However, supplementation can successfully boost vitamin D levels regardless of latitude, results from a new study show.

"These findings highlight a need, particularly in higher latitude countries, for public health and clinical action to improve the vitamin D awareness and status of African-Caribbean populations," say Rebecca M. Vearing, a PhD research student from the Department of Nutritional Sciences at the University of Surrey, UK, and colleagues in their study, published online in the European Journal of Clinical Nutrition.

"As the majority of our vitamin D comes from exposure to sunlight, for many people getting enough vitamin D may be a real challenge," says Vearing in a statement from the University of Surrey.

"This research shows that eating a nutritionally balanced diet including foods that provide vitamin D — such as oily fish, red meat, egg yolk, and fortified foods such as breakfast cereals — and taking regular supplements are key to boosting vitamin D status," she added.

Migration Can Cause Vitamin D Deficiency in Afro-Caribbeans

Studies have shown African-Caribbean populations have relatively low rates of vitamin D deficiency, but importantly, most research on the vitamin D status of those populations has been conducted primarily in countries closer to the equator, where year-round sun exposure is generally high, the authors explain.

They note that Black people, who have a reduced capacity to synthesize vitamin D due to having darkly pigmented skin, may be at a greater disadvantage if residing in regions where their sunlight/UVB exposure is restricted to primarily summer months.

"Migration away from the equator to higher latitudes, and thus reduced sun exposure, has had consequences for vitamin D concentration for populations with darker skin types," they write.

To investigate the collective research on the issue, Vearing and colleagues conducted a systematic review and meta-analysis of African-Caribbean populations living at different latitudes and in different geographic regions. This population refers to those with African ancestry who migrated via the Caribbean or those native to the Caribbean with African ancestry.

They identified 19 articles published between 2005 and 2019 involving 5670 African-Caribbean participants from six countries. Ten of the articles involved populations in Caribbean islands (n = 3209), while the other studies included populations at higher latitudes including the United States and United Kingdom.

The studies showed that average levels of 25(OH)D, the major circulating form of vitamin D, overall were 67.8 nmol/L, with levels > 50 nmol/L deemed sufficient.

But populations residing at high latitudes, such as the United States or United Kingdom, had insufficient mean concentrations of 40.9 nmol/L.

In regions closer to the equator, mean levels were sufficient, coming in at 76.4 nmol/L, with the exception of those participants with type 2 diabetes and those undergoing hemodialysis.

Overall, the dietary intake of vitamin D was poor, with levels of just 3.0 μg/day.

But again, the level of sufficiency was relative to the latitude: the average intake at high latitudes was 5.5 μg/day, however that level is well below the recommended intake in those regions.

In the United Kingdom, for instance, the recommended vitamin D nutrient intake is 10 μg/day, the authors report.

Conversely, levels of vitamin D intake were reported to be sufficient in two of three studies that were conducted at latitudes closer to the equator, including Brazil, where the recommended dietary intake is just 2.5 μg/day in some areas.

"The findings of this review suggest that awareness of vitamin D deficiency needs to be raised amongst African-Caribbean populations living at higher latitudes," the authors write.

"Furthermore, vitamin D deficiency should also be of concern at lower latitudes, as although deficiency rates are lower, sufficient sun exposure may be difficult for some to achieve and others may be predisposed to deficiency due to associated chronic conditions."

They add that "further studies on the association between vitamin D and health outcomes, using larger sample sizes, is needed in this population, especially at higher latitudes."

Brazilian Women Benefit From Supplementation at Low and High Latitudes

In a separate article published online in the Journal of Nutrition, Marcela M. Mendes, also of the University of Surrey, and colleagues, investigated the effects of latitude on vitamin D supplementation among healthy Brazilian women. They conducted two identical parallel trials of 120 women who resided either in the high-latitude United Kingdom or low-latitude Brazil.

In the double-blind trials, women in both settings were randomized to receive a vitamin D supplement of cholecalciferol 15 µg/day or placebo for 12 weeks during the winter.

The results showed that supplementation was similarly effective at increasing and maintaining vitamin D levels in the groups at both latitudes, with average 25(OH)D concentration increasing from 75.1 to 84.8 nmol/L (P = .004) in the Brazilian group and from 38.1 to 55.1 nmol/L (P < .001) in the UK group over the course of the study.

Meanwhile, no significant changes were observed in the placebo groups.

Compared with the placebo groups, the increases in the supplementation groups were significant in the United Kingdom (P = .0002) and Brazil (P = .0035), and the strongest increases were observed among women with the lowest initial vitamin D levels.

"Moderate supplementation of 15 µg/day of cholecalciferol, in accordance with correct recommendations, supports an adequate vitamin D status in adult women, irrespective of latitude and might concomitantly prevent an increase in parathyroid hormone," the authors conclude.

Susan A. Lanham-New, a co-author on both studies, has reported receiving honoraria for three conference talks from Thornton & Ross and one from the Council for Responsible Nutrition, consultancy for General Mills, and is research director of D3Tex, which holds the UK and GCC patent for the use of materials for vitamin D prevention in populations who dress for cultural style. The other authors have reported no relevant financial relationships.

Eur J Clin Nutr. Published online July 19, 2021. Abstract

J Nutr. Published online July 13, 2021. Abstract

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