Daily Dairy Doesn't Improve Bone Strength in Midlife Women

Pam Harrison

June 02, 2020

Dairy consumption does not improve bone mineral density (BMD) or reduce the risk of osteoporotic fracture in women charting menopause, a new analysis of the Study of Women's Health Across the Nation (SWAN) indicates.

And this was regardless of baseline menopausal status, say Taylor Wallace, PhD, George Mason University, Fairfax, Virginia, and colleagues in their article published online in Menopause.

"Our previous work indicated a potential premenopausal critical window in regard to the effectiveness of calcium supplements," they note.

Asked by Medscape Medical News to comment on the findings, Clifford Rosen, MD, professor of medicine, Tufts University School of Medicine, Boston, Massachusetts, said he believes the study reinforces earlier work that dairy intake in women 45-55 years of age does not affect the rate of bone loss or fractures.

"The SWAN study is longitudinal and with sufficient numbers to support their conclusion," Rosen said in an email.

SWAN Study: White Women Consume the Most Dairy

As dairy is known to be one of the foremost sources of calcium, along with other bone beneficial nutrients, Wallace and colleagues decided to examine intake of this food type with long-term bone health using the SWAN data.

The SWAN bone substudy started in 1996 and involved 3302 pre- or early perimenopausal women between 42 and 53 years of age. The sample size for the annualized rate of BMD loss and fracture analysis involved 1955 women.

A modified food frequency questionnaire was used at baseline, at visit 5, and again at visit 9 to record daily dairy consumption, among many other food items.

"Women were classified into four dairy groups based on this cumulative average dairy intake," Wallace and colleagues note. Intake was grouped into < 0.5 servings/day; 0.5 to < 1.5 servings/day; 1.5 to < 2.5 servings/day, and ≥ 2.5 servings/day.

"Non-Hispanic white individuals were more likely to consume higher amounts of dairy compared to African American, Chinese, and Japanese individuals," the authors note.

They found no significant differences for baseline age, BMI, femoral neck and lumbar spine BMD, calcium supplement use, or fracture history by dairy intake group.

Table. Annualized Rate of BMD Loss by Frequency of Intake (Fully Adjusted)

  Dairy Servings Per Day 
  ≥ 0.5 to < 1.5 ≥ 1.5 to < 2.5 ≥ 2.5
Femoral neck, g/cm/y      
Complete cohort –0.00022 0.00004 –0.00042
Premenopause 0.00001 0.00018 0.00011
Perimenopause –0.00038 0.00004 –0.00089
Lumbar spine, g/cm/y      
Complete cohort 0.00005 0.00015 0.00068
Premenopause –0.00028 0.00011 0.00092
Perimenopausal 0.00056 0.00031 0.00052

There were also no differences in the hazard ratios or relative risk of nontraumatic fractures by frequency of daily dairy intake.

Table. HRs for Number of Fractures in Two Groups of Dairy Servings Per Day

  Dairy Servings Per Day 
  < 1.5 (reference) ≥ 1.5
Model 1, hazard ratio 1.00 0.52
Model 2, hazard ratio 1.00 0.89
Model 1: adjusted for all possible confounders. Model 2: additionally adjusted for cumulative days spent in postmenopausal period.
 

Table. Relative Risk of Nontraumatic Fractures (Fully Adjusted)

  Dairy Servings Per Day
  < 1.5 (reference) ≥ 1.5
Relative risk 1.00 0.75

Findings on Dairy and Bone Are Inconsistent

The authors caution that several factors should be taken into account when considering these new findings.

"First, dairy intake was low [overall] among SWAN participants, with 65% reporting consumption of < 1.5 servings/day," they point out.

Dairy intake was also "particularly low" among racial groups other than whites, which may be due to higher rates of lactose intolerance among ethnic minorities, they speculate.

They previously reported that the use of calcium dietary supplements in SWAN was associated with a lower annualized rate of femoral neck BMD loss as well as BMD loss at the lumbar spine over 10 years of follow-up, mainly in women who were premenopausal at baseline.

But no associations were observed in the risk of bone fracture in any women in that analysis, regardless of menopausal status.

In this new analysis, there were no significant differences in calcium supplement use across the dairy intake groups.

Wallace and colleagues also note that the relevance of dairy product intake for bone health has been in question as some observational studies have even "suggested consumption to be associated with an increased risk of fractures."

The lead author of one of these studies, Karl Michaelsson, MD, PhD, of Uppsala University, Sweden, told Medscape Medical News that his study had looked only at milk intake, and the lack of benefit on bone health from high milk consumption may not apply to all dairy products.

We "may need to look at different types of dairy products," he said.

Summing up, Stephanie Faubion, MD, MBA, medical director of the North American Menopause Society, said the new SWAN findings do add to the evidence base, "albeit inconsistent...suggesting a lack of benefit from dairy intake on BMD and fracture risk."

Vitamin D Data Were Not Available; Dairy May Help in This Respect

Rosen also noted that no information was available on vitamin D levels in patients involved in SWAN, which he believes is a limitation of the study.

Nevertheless, "it is important to recognize that elderly individuals who increase their dairy intake may have health benefits as recognized in the Nurses' Health Study, possibly due to increased protein intake, higher vitamin D levels, or greater calcium intake," he observed.

A randomized trial of enhanced dairy intake in long-term care residents is currently underway, which should provide answers for a much more vulnerable population than those in the SWAN cohort, Rosen concluded.

Wallace has reported serving on the scientific advisory board of The Vitamin Shoppe and has received research support from the National Dairy Council and scientific consulting fees from several food companies. Rosen has reported no relevant financial relationships.

Menopause. Published online May 11, 2020. Abstract

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