In October, Prudential Financial released a "financial wellness census" that found women, on average, save 43 percent less for retirement than men. To anyone paying attention, this wasn't entirely surprising, as previous studies have reached the same conclusion.

Why is this disparity such a persistent problem?

Some studies point to the simple fact that women continue to make less money than men. But some people who have studied the issue say there is more going on under the surface.

For many women, societal taboos may be keeping them from being as financially assertive as men. "Folks will say that there is a wealth gap because of the wage gap, but there is also a confidence gap," said Marguerita (Rita) Cheng, CEO of Blue Ocean Global Wealth in Gaithersburg, Md., who has written extensively about the retirement savings gap. 

Cheng insisted there is a "money silence," especially among women. This silence, Cheng said, "prevents women from discussing money matters. While women have gained influence and affluence, these taboos hold women back."

Indeed, a recent Federal Reserve study found that 60 percent of college-educated, not-yet-retired men are comfortable managing their investments, while only 35 percent of women can say that.

What can be done to close the gap, to better prepare women for retirement expenses? What should advisors do better or differently?

"Financial professionals have a key role to play here in helping women to develop retirement income strategies that meet their retirement goals and help women to realize the lifestyle they want in retirement," said Sluyter. "[But] 66 percent of women don’t work with a financial advisor, either because they believe they can’t afford it or [they believe] they don’t have adequate resources to warrant an advisor’s help."

No doubt advisors can do a better job of meeting women clients' needs, too. "Sure, women—no matter their age or relationship status—should take a more [active] role in their financial lives," said Cheng. But, she stressed, it's also important for advisors to "create a judgment-free zone for women to ask questions, so they can feel more financially confident and empowered."

Women, she said, tend to think in a "more relational manner, as opposed to a linear" manner, than men. They often prefer a "holistic and comprehensive approach toward managing money," she added. "Financial advisors should invite women to be part of the conversation."

Industry officials agree that more needs to be done about the issue.

"The disparity in retirement savings for women is deeper than what's at face value," said Kent Sluyter, president of Prudential Annuities. "We have made enormous strides in closing the gap. But for women, who are increasingly bearing more responsibility as primary wage earners and ‘CFOs’ of their household, it is even more important to help close the retirement income gap."

The Prudential report found that women and men, on average, expect to retire at age 67. But the average woman in the survey saved just $115,000 for retirement, compared with $203,000 for men. Nearly half (46 percent) of the women said they had no retirement savings at all. This is particularly startling since women tend to live longer; their need for retirement income is even greater than men's.

The gap may start early, too. Women now graduate from college in higher numbers than men but, as a consequence, they also hold 64 percent of all student debt, the Merrill study found. This inequity is further compounded by the gender pay gap. Women earn about 78 percent of what men do.

"Women’s average earnings—both annual and lifetime—remain below the level of men’s," said Sluyter. "Lower earnings during working years have also resulted in women earning Social Security benefits that are 23 percent lower than men’s, which is a key contributor to the retirement income gender gap. Currently, the median annual income of women age 65 and older is 42 percent lower than men's."

Further complicating women's lifetime earnings potential is the fact that many women interrupt their careers for parenting or, later, taking care of their parents.

"Divorce further compounds the risk," noted Sluyter. "More than a quarter of women say their spouse’s money will be a significant source of retirement income. But with just 45 percent of women married by age 65, compared to 70 percent of men, it pays for women to be individually prepared to tackle the retirement income challenge."